DW172: Specification for Kitchen Ventilation Systems - PDF Free Download (2024)

HVCA Heating and Ventilating Contractors' Association

DW/1 72 Sped! leation for Kitchen Ventilation Systems

Specification ACKNOWLEDGEMENTS The HVCA records its appreciation and thanks to the

many people and organisations who gave advice and

information during the preparation of this

f o r Kit C 11111 en

Ventilation S yst e rn s

specification, in particular to those members of the drafting panel who contributed their time, experience and knowledge.

DW/172 DRAFTING PANEL Keith Waidron (Chairman)

Phil Gibson

Barry Pollard Peter Rogers Nigel Atkinson

Trevor Carter Steve Garnham

Graeme Craig (Secretary)

ISBN 0-903783-29-0

First Edition 1999

©2005 HVCA

Heating and Ventilating Contractors' Association Esca House 34 Palace Court London W2 4JG Tel: 020 7313 4900 Fax: 020 7727 9268

DgJ/ I 7 2 e-mail:

[emailprotected] website: www hvca.org.uk 1

DW/1 72 Specification for


Kitchen Ventilation Systems

DW/1 72 Specification for Kitchen Ventilation Systems


Barry Pollard

Chairman, Ductwork Group Heating and Ventilating Contractors' Association


ince its publication in 1999, the HVCA ' Standardfor Kitchen Ventilation

Systems (DW/171) has sold an impressive 2,300 copies. More importantly, it has become widely acknowledged as the standard for kitchen ventilation design throughout in the UK. Like any other standard, however, it must be revised and updated from time to time, in the light of new thinking, new procedures and new developments. This review process has now been completed by the 1-IVCA Ductwork Group. The result is this new publication— designated DW/ 172 and re-badged as a specification rather than simply a standard, in recognition of the authoritative status it has achieved within the kitchen ventilation sector. Among the many amendments and clarifications contained in the new document, three are worthy of particular note. Firstly, the previous publication made reference to the feasibility of establishing a test procedure for grease filters. Since then, the Loss Prevention Council has published — and the Association of British Insurers has endorsed — LPS 1263, which sets out the procedures, including the testing and grading of grease filters, required to reduce the risk of fire in commercial kitchens. Secondly, the section on appliances and their coefficients has been significantly expanded, and now includes advice on the requirement for an interlock between the ventilation system and the gas supply. And, finally, for the purpose of this specification, stainless steel is the only suitable material for the fabrication of canopies, and mesh filters can only be used as a secondary method of grease extraction. For ventilated ceilings, however, some manufacturers incorporate anodized aluminium into the supporting frame. This form of construction should be agreed with the client or specifier. All other sections have been revised and updated in the hope and expectation that the HVCA's Specfi cation for Kitchen Ventilation Systems (DW/172) will be widely used by all sectors of the catering industry.


DW/1 72 Specification for


Kitchen Ventilation Systems

DW/1 72 Specification for

Kitchen Ventilation Systems


Section 1

Acknowledgements Drafting Panel Foreword Specifications and Contents Introduction.

Section 2 Considerations prior to design Section 3 Design Criteria Section 4 Canopy Dimensions

Page 1 1

3 5 7

8 9 11

Extract Flow Rates


Section 6 Make-up Air Section 7 Types of Canopy Section 8 Ventilated Ceilings Section 9 Spigot Connections Section 10 Materials Section 11 Construction Section 12 Polishing Section 13 Grease Filtration

17 20

Section 5

Section 14 Canopy Lighting Section 15 Ductwork Section 16 Installation Section 17 Fans Section 18 Attenuation Section 19 Dampers Section 20 Fire Suppression Section 21 Service Distribution Units Section 22 Odour Control Section 23 Heat Recovery Section 24 Testing and Commissioning Section 25 Cleaning and Maintenance Appendix A Filter Classifications Appendix B Conversion Factors Appendix C IP Ratings Appendix D Fire and Smoke Extract Ductwork Appendix E Air Conditioned Kitchens Appendix F Bibliography

22 26

27 28 29 29 34 35 38 39 42 42 43

46 47 49 50 51 53

54 55 56 58 60 5

DW/1 72 Spec ijicatioii for

Kitchen Ventilation Systems

OBJECTIVE The satisfaction derived from a building by the user


comes significantly from the satisfactory performance of the systems, which serve the building. The purpose

DW/143 A Practical Guide to Ductwork Leakage Testing

of the kitchen ventilation systems is to remove DW/144 Specification for Sheet Metal Ductwork contamination from the cooking processes, ventilate the surrounding ancillary areas and provide safe and comfortable conditions for the occupants. This publication is therefore primarily intended to: - Provide information for customers who are

Low, Medium & High Pressure/Velocity Air

Systems DW/154 Specification for Plastics Ductwork

DW/172 Specification for Kitchen Ventilation Systems

appointing (by competition or negotiation) a DW/191 Guide to Good Practice contractor.

- Provide a specification for kitchen ventilation TRI19 system installation. - Provide a level of workmanship that may be verified by independent assessment. - Be a significant aid in producing installations that will, given correct operation and with proper maintenance, provide satisfactory service over many years.

QUALITY ASSURANCE This specification can be used as one criterion that will

assist customers and specifiers in performing their important role of defining the standard of installation they require. The HVCA anticipates that this specification will be

complementary to quality assurance schemes and quality assessment schedules. Where forming the basis of an independent certification scheme, it defines good practice in standards of installation.

SCOPE This specification covers the type of kitchen ventilation systems usually found in commercial premises.

The specification is not intended for residential premises, although some of its provisions will apply.

This specification makes use of terms "should", "shall" and "must" when prescribing procedures: - The term "must" identifies a requirement by law at the time of publication. - The term "shall" prescribes a procedure which it is intended to be complied with, in full and without deviation. - The term "should" prescribes a procedure which it is

intended to be complied with unless, after prior

consideration, deviation is considered to be equivalent or better.

PUBLICATION AND REVIEW User feedback on the wording or the requirements of

the specification will be welcomed to assist in continued updating.


Glass Fibre


Guide to Good Practice - Cleanliness of Ventilation Systems

DW/1 72 SpecifIcation for Kitchen Ventilation Systems

• Air is required to dilute and replace


products of combustion from gas fired appliances.

Introduction 1.1

• Supply air is required to ensure complete combustion of the fuel and provide safe operation of the gas equipment. Details of these requirements are contained in the Building Regulations, BS 6173 and the

A cooker canopy is currently defined by the CEN European Standards Committee as being a device intended to collect contaminants from above a cooking appliance and remove them

from the room. In practice kitchen canopies have become much more than basic extract systems.


CIBSE Guide B2.


gas-fired catering appliances for use in all types of catering establishments (2nd and 3rd family gases), includes a requirement that gas fired catering appliances cannot be operated

The prime function of a kitchen canopy is to

protect the area surrounding the cooking process from soiled matter and flame to make

without the kitchen ventilation system in operation. Therefore an air proving device shall be installed in the kitchen ventilation

tolerable and safe the immediate area for people to work in. An air flow shall be created

across the cooking process to capture the fumes created, and the by-products of this vapour shall be collected and contained by

system and interlocked with the gas supply for the kitchen. The kitchen ventilation contractor shall be specifically responsible for providing the air proving mechanism.

means of the filters within the canopy, allowing the cleaner air to be discharged.



Food Safety (General Food Hygiene)

1 .7

identified and that steps are taken to ensure

• Smoke

that adequate safety features are in place. Part

• Expanded air from the heat load

of that process requires that there must be

surrounding the cooking device.

suitable and sufficient means of either natural or mechanical ventilation.

• Precipitation of moistures existing in the

food into a vaporous state, primarily

The Workplace (Health, Safety and Welfare)

consisting of steam, grease and cooking

Regulations also require that 'an effective and suitable provision must be made to ensure that every enclosed workplace is ventilated by a sufficient quantity of fresh air'.

1 .5

The four main emissions that require removal


Regulations place an onus on the proprietor of a 'food business' to ensure that all hazards are

1 .4

The British Standard BS 6173, Installation of

Ventilation is required in both the kitchen and

the adjoining areas because:


• Exhaust fumes from combustion appliances such as gas, charcoal or mesquite.


• Considerable convective and radiant heat is given off by the cooking equipment.

• The air becomes laden with odours, grease fumes and products of combustion.

• During meal preparation and washing up, humidity is increased over a wide area.

The removal of these cooking vapours and the supply of make-up air together with details of those ancillary services that can be supplied by

the kitchen ventilation contractor, are the topics to be covered by this publication.


Although this Specification has been written with commercial kitchens in mind, many of the aspects covered and recommendations made, may also apply to domestic kitchen situations.

• Air replacement and consistency of temperature are required in adjoining areas.


DW/1 72 Speci/ication for Kitchen Ventilation Systems

SECTION 2 Considerations prior to design 2.1

In order for the most economical and effective design to be prepared, it is important that the following information must be made available to the designer:

• The type, size and power source of the appliances being ventilated. If gas, the requirements of BS 6173 shall be met.

is required, and if so whether it is to be supplied through the canopy, through the HVAC system or a combination of both.

• Where air is supplied through the canopy, is

it to be by means of front face grilles, perforated plate diffusers or internal slot discharge.

• Details of access into the building so that the number of sections in which the canopy is to be fabricated can be determined. The

availabl.e headroom and ceiling height where appropriate are essential.

• The layout of the appliances and their power consumption where known.

• The position of discharge to ensure that

• The dimensions, height and layout of the room that contains the appliances to be

• The amount of air to be handled by the


• Whether ventilation is to be provided by means of a canopy or ventilated ceiling.

• If a canopy, is it to be at high or low level, wall or island mounted.

• Where a ventilated ceiling is to be used, whether a plenum or modular cassette type is required, at what height it should be set

and the level of services running through

the ceiling void (to include floor to preferred finished ceiling height and floor to slab height).

• Whether grease is being produced in the cooking process and if so, whether filtration is to be provided by means of baffle filters, cartridges, water wash or cold water mist. If

grease is not produced, whether the extraction point can be fitted with a baffle plate or grille.

• Whether the ductwork is to be constructed to either DW/ 144 or a fire ratedlsmoke exhaust specification and whether the fans have to be fire rated.

• Whether lighting is required within the canopy or ceiling, and if so what type.


• Whether mechanically powered make-up air

noise or odour does not create a nuisance.

canopy or ceiling. This will determine the type, size and number of filters and spigots required.

• Whether approvals from the


Authority have been obtained.

• It is now known that some cooking processes, where there is incomplete degradation of certain organic materials, generate fumes which are carcinogenic.

This is possible irrespective of size of kitchen, and it is therefore important to ensure that there is an effective ventilation system for all cooking operations to ensure

the health and safety of the kitchen personnel. Care shall be taken to avoid drawing extract air through the breathing zones of members of staff operating the cooking equipment. Care shall always be taken if discharging into a public area is necessary.

• The method of internally cleaning the inside

surface of the ductwork extract system, which, in turn, will determine the size of access panels and their frequency.

DW/1 72 Specification for Kitchen Ventilation Systems


selected for either room distribution or spot

cooling around the canopy or ventilated ceiling. The ideal discharge temperatures for the various supply options are shown in Table

Design criteria 3.1

Whilst differing design approaches exist to

Table 1: Discharge Air Temperatures providing a solution which satisfies the outside ambient ventilation requirements of a kitchen, the Inboard canopy supply air following methodology has been found to Outboard canopy supply air provide a satisfactory outcome and is proposed Ventilated ceiling supply air

as a suitable procedure to adopt to achieve a HVAC general make-up air satisfactory design.

• At the time of publication of this 3.5 Specification, no legislation exists in the UK regarding maximum permissible room temperatures in the workplace. Even with the most efficient ventilation systems, air temperatures taken in the kitchen in the proximity of the cooking equipment could

be ventilated to avoid the potential health

converted to convective, sensible heat.



work surface.

• Dedicated make up air systems to be 85%

an average over 8 hours.

maximum, of the extract flow rate.

canopy or ventilated ceiling.


speed regulation can also enhance energy efficient use of the system and plant Variable

when there is partial or low load cooking conditions. However, care shall be exercised in



Whilst the ventilation of ancillary areas would

normally fall within the scope of the main ventilation system, the following notes are included for the guidance of the designer.

3.7.1 Cold Rooms - It is important to establish whether the compressor/condenser sets are to be located:

maintaining correct velocities through the

a) On top of the Cold Room and above the

grease filters when cooking is in process. For recommended face velocities see Table 13.

b) Built into the Cold Room and discharging

Whilst these criteria are ideal, it is unlikely to

c) Mounted externally and remote from the

achieve a controlled environment within a kitchen due to the natural but varying heat


Fresh air ventilation rates must be sufficient to

ensure that the CO exposure levels to which the kitchen staff are subjected do not exceed the COSHH limits of 300 parts per million (ppm) for 10 minutes, or the World Health Organisation (WHO) guide-lines of 10 ppm as

• Average lighting levels of 500 lux at the

• Minimum air change rate of 40 per hour not to be used as a basis of design of the

Humidity is also difficult and expensive to control, but the ventilation system should be

into the environment. Dishwashers shall also

heat from the cooking equipment being


minimum lOdegC' minimum 16 degC minimum 16 degC

designed to provide a sufficient ventilation rate to maximise comfort. With particular reference to dishwashing machines, unless provided with their own condensers, these machines shall be provided with dedicated extract ventilation to control the amount of vapour being discharged

be well in excess of 28 degC due to radiant

• Internal noise level should be from NR4O -



into the area. Cold Room.

gains from the cooking equipment.

When cold room condensers discharge directly into ceilings or rooms, then they should have

Staff comfort should be a prime consideration

individual extract and possibly dedicated

when designing a make-up air system. The supply air temperatures should therefore be

supply systems.


DW/1 72 Specification for

Kitchen Ventilation Systems

3.7.2 Dry Stores - A ventilation rate of 10 air 3.7.8 Kitchen - For areas within larger kitchens that changes per hour is recommended. If the room door leads on to the kitchen area, mechanically

are not affected by canopies or covered by the areas described in 3.7.1 - 3.7.7, then a general

introduced supply air and a transfer grille at low level in the door should be provided to

ventilation rate of 40 air changes should be used.

relieve the air for capture by the kitchen


exhaust system.


dedicated machine extract, general room A ventilation rate of 12 air changes per hour is recommended but great care should

extract should also be considered. A

be taken with the position of grilles and diffusers. The servery is usually located


Servery -

between the kitchen and the dining area. The

ventilation rate of 30 air changes per hour is


be taken from 'dirty' areas such as waste

display cabinets, and the fact that the ceiling

storage areas or pot wash rooms. Care should also be taken that unwelcome draughts are not created around customers. Make-up air shall not be drawn from an adjacent eating area if smoking is permitted.

Chef's Office -

A ventilation rate of 6 air

changes per hour is recommended but comfort cooling may be considered desirable as the area

is often used as a dining facility for visitors. Privacy should be maintained by avoiding the use of transfer air grilles.


Refuse Store - The Local Authority should be

consulted for their particular requirements, but

a dedicated extract system providing a minimum of 15 air changes per hour is recommended.


Preparation Areas - The treatment will depend

upon the type of food being prepared and whether these areas are 'open' to the kitchen or

whether a separate room is to be provided. Where open to the kitchen then the overall air change rate should be sufficient, with supply

air introduced to the preparation area itself.

When very low room ambient space temperatures are required then a separate area is required. Where low room temperatures are not required, then a ventilation rate of 20 air changes per hour is recommended.


Toilet Areas - Whether for food handling personnel or customers, separate and dedicated

extract systems with duplicate fans shall be installed for toilet areas. A ventilation rate of 10 air changes per hour is recommended. Negative pressure should be maintained in all toilet areas at all times.


Mechanically powered make-up air should not

number of people, the heat from the food, may well be lowered to provide an architectural feature will all affect the design. Too much air movement may cause 'skinning' and cooling of the food. Too little will result in discomfort for both kitchen staff and the customers.


Dishwash and Potwash Areas - In addition to


Diversity factors shall not be applied to reduce

the extract flow rate calculated from Table 2 when partial or intermittent use of appliances is proposed.

DW/1 72 Specification for




be given to increasing the face velocity to

compensate irrespective of design duty

dimensions of a canopy are invariably

calculated. It is also recommended to increase the size of the canopy to aid capture when the ideal flow rate cannot be achieved.

determined by the size of the catering equipment that it is serving.


Unless restricted by walls, the plan dimensions

of the canopy shall always exceed the plan dimensions of the catering equipment by a

less than 400mm high will be less efficient than normal because of a reduced Canopies

collection volume and therefore, where there is a restricted soffit height, consideration should

Canopy dimensions 4.1

Kitchen Ventilation Systems


With kitchens that have high ceilings, provided that the canopy is installed at the correct height

to allow access to the filters and the

minimum of 250mm on each free side, and by 250mm at the front and rear. It shall be noted that the overhang dimensions are to the inside

requirements for minimum hood depth have been achieved, then consideration should be given to providing an infill section to fill the gap between the top of the canopy and the

of the condensation or stiffening channel, or the supply plenum, the appropriate dimension shall be added when specifying the overall

underside of the ceiling.

canopy size.

Fig 1 - Typical Canopy Dimensions



than 2 100mm, then overhang dimensions shall For combination steamers and certain types of

be increased at a minimum rate of 1:1, i.e.

baking ovens the overhang at the front should be increased to a minimum of 600mm to cope

100mm vertical + 100mm horizontal.

with the steam or fumes released when the 4.8

primarily by the ceiling height. The underside of the canopy should be located between 2000

The distance between the lowest edge of the grease filter and the top of the cooking surface should be 450mm minimum. This is to avoid the risk of excessive temperatures or fire in the filter which could cause the extracted grease to vaporise and pass through to the ductwork.

and 2 100mm above the finished floor level, the

This dimension will vary with the type of

doors of the appliance are opened.


Where a canopy is installed at a level higher

The height of the canopy is often governed

top should project into the ceiling by a

cooking appliance and may be reduced where a fire suppression system is fitted.

minimum of 25mm to allow the false ceiling trim to be attached. (see illustration in fig. 1).



gas-fired salamander grills are

mounted at high-level in close proximity to the


DW/1 72 Specification for

Kitchen Ventilation Systems

grease filters/extract plenum of a canopy, the

manufacturer of the grill should supply a deflector cowl for the flue opening on top of


the grill. This will encourage products of combustion to be directed away from the

Extract flow rates

canopy and cool prior to being drawn through

Extract and Supply Air Flow Rates

the filters. This will reduce the potential of fire-flares, which are known to occur with 5.1 such appliances, being drawn into the grease filters to possibly ignite grease and oil deposits It will also help to prevent beyond. discolouration of the stainless steel surfaces immediately above these grills and carbonisation of deposits on the grease filters.

Whilst systems extracting from equipment producing contaminant such as dust depend upon air streams of sufficient velocity being created to enable capture to take place, this concept cannot be applied to a heat producing

process such as cooking. All cooking processes create approximately 35% radiant and 65% convected heat which, in the absence of cross-draughts, rises vertically in a thermal

updraught called a 'plume'. This is shown in fig 2. Most of the contaminant released from the food and heat source is entrained with

additional air which causes the plume to enlarge and the average temperature and velocity to decrease. The rate of exhaust from the hood shall equal or slightly exceed the flow

rate of the plume, additional extract air (see Table 3; Canopy Factors) will be required to resist the cross-draughts that would otherwise carry the plume away from the canopy. CANOPY


Hkk i





Fig 2 - Air Flow Pattern


The calculation of the optimum extract flow rate is the most important element of canopy

design as too much air will cause as many problems as too little. Whilst the size of the cooking appliances determines the size of the

canopy to be supplied, it is the type of appliance that determines the volume of air to be extracted. Those that require ventilation are shown in Table 3.


DW/1 72 SpecifIcatiw for

The 'Thermal Convection Method' of

Kitchen Ventilation Systems

extracted. The factor will vary depending on whether the appliance is gas or electricity, and these are scheduled in Table 2. Refer to 5.4 for worked example of flow rate calculation.

calculation should be the only method used.

Other methods have been included in this document for use only when insufficient information is available at the design stage (see sections 5.5 to 5.8).

The theoretical extract air volume would only

be achieved under draught-free laboratory


Method I - Thermal Convection

conditions. The type, location of the


canopy/ventilated ceiling and the likelihood of

This method follows the procedure covered in

cross-draughts will also have an affect upon the amount of air required. The more enclosed the cooking operation, the less the exhaust air needed to ventilate it, whilst appliances open on all four sides will need a larger volume of exhaust air than where only one side is open.

the CIBSE Guide B2 but has been expanded to

include a wider range of equipment. When details of the equipment to be ventilated are known, then each cooking appliance shall be allocated a thermal convection coefficient,

The canopy factors given in Table 3 shall therefore be multiplied by the calculated volume to determine the actual extract flow

which is the recommended volume of air to be extracted in m3/s per m2 of surface area of the

appliance. The area of each appliance is

rate. Consideration shall also be given to the 'active area' of ventilated ceilings when the height increases. See Section 8.5.2.

multiplied by the factor for that appliance, the total value for each item of equipment under

the canopy/ventilated ceiling shall be added together to determine the total volume to be

Table 2: Appliance, Coefficient and Temperature Schedule Appliance

Coefficient Gas Electric


Surface Temp

m3/sper m2 0.03 0.15 0.30 0.40



25 25 57

25 0.03 Benches, Spreaders and Worktops 25 Sink 0.15 0.30 61 Pass Through Dishwasher* 42 0.40 Pan/Utensil Wash Machine see manufacturer's literature 58 Rack and Flight Dishwasher *NB - the figures quoted are for the machine only, the room in which they are located needs to be treated

separately. HEATING/WATER

Coffee Maker Microwave Oven/Toaster Bains Marie, Hot Cupboard Servery Counter - Hot Food Water Boiler/Still/Beverage Unit Light Duty Boiling Pan, Tilting Kettle Refrigeration Unit

0.20 0.24 0.25 0.30

0.03 0.15 0.24 0.20 0.25


78 98

see manufacturer's literature continued overleaf


DW/1 72 Specifkatioii

for Kitchen Ventilation Systems


0.10 0.25 0.20 0.30 0.20 0.30 0.20 0.32 0.26 0.35 0.25 0.35 0.25 0.35 0.25 0.35 0.30 0.35 0.30 0.35 0.30 0.38 0.30 0.38 0.30 0.45 0.35 0.50 0.30 **NB - multiply the coeffIcient factors by 2 f ovens are double stacked.

Induction Rob, Ceramic Stove Pastry and High Output Bakery Oven** Steamer/Pressure Cooker Pasta Cooker Bratt Pan, Tilt Skillet Boiling Table, Hob Top, Stock Pot Stove Heavy Duty Boiling Pan Open Top Range and Oven Steaming and Roasting Oven Combination Steaming Ovens** Tandoori Oven Fan Assisted Convection Oven** Pizza Oven** Low/Med Duty Deep Fat Fryer Low/Med Duty Grill

30 86 125 120 190 190 146 190 98 92 90 86 92 190 220


Griddle (mild steel) Griddle (chrome) Conveyor Pizza Oven Heavy Duty Deep Fat Fryer Heavy Duty Bratt Pan Solid Top Oven Range Upright or Chain Broiler Salamander or Steakhouse Grill Rotisserie

Chargrill/Charbroiler Chinese Wok Range Chinese Wok Range (induction) Mesquite Grill

190 290 90


0.25 0.40 0.40 0.45 0.45 0.51 0.55 0.55 0.55 0.52 -



50 420

0.30 0.45 0.45 0.50 0.55 0.60 0.75 0.75 0.75 0.95



240 420 190

260 190 350 280

Table 3: Canopy factors Type Low Level

Passover Overhead Wall Overhead Wall, Island Mounted Island


Open Both Ends

Open One End


1.10 1.10 1.20 1.40 1.25

1.15 1.25

1.50 1.35

Closed Both Ends 1.05 1.05 1.15 1.30 1.15

DW/1 72 Spec/f Icatioii for


Kitchen Ventilation Systems

Example of flow rate calculation: Method 1

Fig 3 - Typical Cooking Equipment Line-Up

1. Determine the mode! type, plan size and power source for each item of cooking equipment located under the canopy.

2. Calculate the plan area of the cooking equipment from Fig 3 and from Table 2, allocate a thermal coefficient for each item

4. Add the individual rates to arrive at a total extract flow rate for the canopy. 5. Select the appropriate canopy factor to suit the type and location of canopy. 6. Multiply the total by the canopy factor to arrive at the total extract flow rate.

of equipment.

3. Multiply the area by the coefficient to obtain a theoretical extract flow rate for each item.

Table 4: Calculations for method I (based on the equipment illustrated in fig. 3J: Area Plan Size Power Item 0.4500 600 x 750 Griddle gas 0.6750 900 x 750 gas Open top range 0.5625 750 x 750 gas Solid Top Range 0.3750 500 x 750 Bench 0.4875 650 x 750 Elec Twin Fryers 0.3000 750 x 400 Salamander Grill gas Theoretical extract volume required Canopy Factor - overhead wall open both ends

Specific extract flow rate required

Coefficient Flow Rate 0.30 0.135 0.236 0.35 0.338 0.60 0.011 0.03 0.35 0.171 0.75 0.225 = 1.116m3/s

x 1.25 =

1.395 m3/s

The calculation of extract flow rates for

above such equipment. In such circ*mstances

ventilated ceilings should be in accordance

care shall be taken to ensure maximum air

with the procedures set out above.

duties are not exceeded for the particular filter bank selected. Make up air and extract spigots shall be sized and positioned accordingly.

Where concentrated high-heat cooking appliances create a possible 'hot spot' within a canopy or ventilated ceiling area, partitioning of the grease filter plenum shall be considered

to provide a higher dedicated extract duty

Following the determination of the required extract flow rate, the number and type of filters shall be selected.


DW/1 72 Specification for


Kitchen Ventilation Systems

Method 2 - Face Velocity Method (This is a

rather than the physical size of the appliance,

provisional method when there is insufficient information available regarding the cooking equipment)

then the power input method may be used.

Each type of appliance is allocated a recommended flow rate in m3/s which is then

multiplied by the power input in kW to determine the flow rate required for each appliance. The total air required is then

The volume of air to be extracted may be determined by selecting a velocity across the face area of the canopy that is appropriate for the type of appliances expected to be used. The capture velocity is multiplied by the canopy

determined by adding


The capture velocity should be selected to ensure an even distribution of air across the canopy is either wall or island mounted. 0.25

mIs. Applies to

steaming ovens, boiling pans, bains marie and stock-pot stoves.

• Medium loading -


• Heavy Loading -


high as 60 - 120 to be created when highoutput equipment is densely located in a

mIs. Applies to

deep fat fryers, bratt pans, solid and open top ranges and griddles.

relatively small space.


mIs. Applies to

chargrills, mesquite and specialist broiler units.


Method 4 -Air Changes (This is a provisional method when there is insufficient information available regarding the cooking equipment)

These can vary widely depending on the size of kitchen, type of cooking, number of people present, and therefore not recommended as a method of calculating air volumes. Whilst 40 air changes per hour should be regarded as a minimum for comfort in the absence of any other information, it is not unusual for rates as

canopy face, this velocity will vary according

to the cooking application and whether the

• Light loading -



area to determine the volume of air to be extracted.


recommended extract rate for each item of

Method 3 - Appliance Power Input (This is a provisional method when there is insufficient information available regarding the cooking equipment)

When details of the cooking equipment to be

Method 5 - Linear Extract (This is a provisional method when there is insufficient information available regarding the cooking equipment)

Favoured in the United States, this method depends upon selecting a flow rate to suit a particular type of canopy. The figures, which are listed in the Table 5, do not vary with the canopy width and are given in m3/s per linear metre of active filter length.

used is limited to the amount of power required

Table 5: Flow rates (m3/s per linear metre of canopy) Type of Canopy Wall_Mounted

Single Island Double Island Eyebrow Passover/Backshelf

Light Duty 0.23 - 0.31 0.39 - 0.46 0.23 - 0.31 0.23 - 0.39 0.15 - 0.31

Medium Duty 0.31 - 0.46 0.46 - 0.62 0.31 - 0.46 0.23 - 0.39 0.31 - 0.46

Heavy Duty 0.31 - 0.62 0.46 - 0.93 0.39 - 0.62

Extra Heavy Duty 0.54 + 0.85 + 0.77 +

0.46 - 0.62

not recommended

NB - Extract rates for double island canopies are for active filter length, i.e. double the rate for an equivalent length wall Canopy


DW/172 S;7 f'/c. for Kitchen Ventilation Systems



a combination of all three. Where air is introduced through the canopy, the various

In order for the kitchen extract system to

function correctly, it is essential that an

allowance shall be made for the provision of 6.4 replacement air. This should be achieved either by introducing mechanical supply air, or by making provision for natural infiltration.

Where a natural ducted inlet for relief air is selected it should be as short as possible, at

high level and with filtration since the incoming air is likely to be contaminated.


air may be introduced into the

kitchen by means of the canopy or ventilated ceiling, or through the ventilation system or by

Make-up Air 6.1


Where mechanical input is selected, the system

shall provide a maximum 85% of the total extracted volume, with the remaining 15% infiltrating naturally into the kitchen from surrounding areas. The mechanical or 'fan assisted' method should ensure that the kitchen

remains under negative pressure thus preventing the potential transfer of kitchen

options are shown in Figs 4 and 5.

The fan powered system provides positive control and therefore should be the preferred

method used. With natural infiltration the following problems may occur:

• unfiltered air will enter the kitchen.

• air may otherwise be drawn from dirty areas.

• draughts and discomfort may be caused in cold weather.

• uncontrolled air movement may affect the cooking process.

• 'cooling' cannot be provided to persons adjacent to the canopy.

odours to areas outside the kitchen.

75% TO 85%



TO 85%





Fig 4 - Outboard Supply Systems


DW/1 72 Specification for Kitchen Ventilation Systems


100%+:NTR7NMENT --1

MAX 50%










- 70 /



Fig 5 - Inboard Combined Supply Systems

NB: When the air is inboard then that duty shall be added to the calculated extract flow rate to determine the volume handled by the fan.


Make- Air Temperatures

6.5.1 A minimum air entry temperature of 10°C shall be selected for canopies and 16°C for ventilated ceilings.



For general make-up air, standard

shall be accessible for cleaning. A packaged air handling unit is preferable as individual plant items will present hygiene problems.

• A natural ducted airway allowing outside

temperatures as specified in Section 3 should be used.

air into the kitchen shall be provided. This again should be positioned at high level, be

When selecting plant for kitchen make-up air,

Care shall be taken with the location of the discharge grille because with low external temperatures, discomfort may be

the following shall form part of the ventilation system:

• Filters made of synthetic materials and having a minimum efficiency of F6 (see Appendix A). Glass fibre products shall not be used.

• Means of varying the fan duty shall be

provided to give the flexibility to

accommodate future changes in room usage, occupancy and types of cooking undertaken. An electrical interlink with the extract plant shall be installed.


• Where located within the kitchen, plant

as short as possible and shall be filtered.

experienced by the kitchen users. This

option should not be selected when large air volumes are involved.

• Whilst door transfer grilles may be used in conjunction with other input systems, there is usually inadequate space to accommodate sufficient grilles to handle

the large volumes of air required with kitchen extract systems. Transfer grilles in

doors however, help to minimise air pressure influences on opening and closure.

DW/1 72 Specification for Kitchen Ventilation Systems

• Visible or audible means of proving the existence and indicating the supply air filter condition shall be installed, as dirty filters will adversely affect the air balance.



a natural make-up air system is

selected, the resistance shall be included in the

Fig 6 - Outside Air

overall system resistance against which the extract fan will have to operate.



shall be taken with re-circulated air to

ensure that it is not taken from 'dirty' areas.



Whilst air conditioned kitchens are the exception in the United Kingdom, where it is decided to cool the make-up air, further details are given in Appendix E. Details




Fig 7- Low Level Wall

of the various types of natural air

transfer systems are shown in Figs. 6-8 below: FD



Fig 8 - InternalAir Transfer

NB. Fire dampers should only be required in fire compartment walls.

DW/1 72 Specification for

Kitchen Ventilation Systems

SECTION 7 Types of Canopy 7.1

The only material to be used in the fabrication

of canopies in accordance with this specification shall be type 304, ultra-fine grained stainless steel.



are a number of types and style of

extract canopy that have been developed; these can be broadly classified as follows:

• Counter type canopy • Eyebrow canopy • Condensation canopy Most styles of canopy can be provided with an integral make-up air facility; these can take the form of:

• Front face perforated diffuser

• Front face grille

• Overhead wall type canopy - wall or island mounted

• Internal slot -

• Overhead island type canopy

• Grille or louvres for spot cooling

• Low level wall type canopy

• Passover type canopy


Induction, entrainment, capture, compensating or short circuit.

Examples of the various types and combinations available are shown in Figs.911:








Fig 9 - Typical Extract Only Filter Canopies.



DW/1 72 Specificarioiz for

Kitchen Ventilation Systems





Fig JO - Non-Filter Canopies





Fig 11 - Condensation Canopies


DW/1 72 Specification for Kitchen Ventilation Systems

Section 8


Modular Cassette System 8.4.1

Ventilated Ceilings 8.1

ventilated ceilings should be considered as a viable option.

system extract, partitioned or dedicated supply, and flush mounted luminaires. The ceiling comprises a grid system which supports extract and supply cassettes, and luminaires. The extract filters, of proprietary design, filter and separate

Ventilated ceilings should also be considered:-

passing into the ceiling void for

incorporating dedicated

Whilst the use of canopies is ideal for handling contaminants produced in concentrated areas, where the cooking equipment generates grease and water vapour over a wider area, the use of

the contaminant from the air before

central collection and discharge to atmosphere. The grease is collected both inside the extract cassette and in

floor to finished ceiling levels make the use of canopies impractical.

a non-drip integral or perimeter trough for removal and cleaning.

• Where false ceiling aesthetics are important


and visibility cannot be impaired by • Where cooking equipment generates low

cooking appliances with blank, supply

food production and food preparation

filters, or luminaires being fitted in


the non-active areas of the kitchen.

The calculation of minimum extract flow rates for ventilated ceilings shall be in accordance with the procedures set out in Section 5 of this


spot cooling.

section 3 and 6.



There are two types of ventilated ceiling

Fig 12 - Cassette Type Ceiling.

cassettes may be integrated

make up air, comfort ventilation or

designed to provide the conditions set out in

• Plenum Ceiling


into the ceiling design to provide

document. The supply system shall be

• Modular Cassette Ceiling

extract cassettes should be

cassettes shall be located over the

levels of discharge over large areas, such as

system available:-


designed for easy removal and sized for cleaning in conventional commercial dishwashers. Extract





• Where due to structural limitations, low


The Modular Cassette type ceiling is a


For secure installations, panels should be lockable.

Calculating Size of "Active" Exhaust Zones


The dimensions of exhaust zones shall

be determined by the size of the catering equipment that it is serving.

DW/1 72 Specification for

8.5.2 The plan dimensions of the exhaust

Kitchen Ventilation Systems

possibility of 'thermal cooling' of the rising particles back to solid matter, thus stopping the grease returning to work surfaces.

zones should exceed the plan dimensions of the catering equipment.

As the finished ventilated ceiling height increases, consideration should

be given to either increasing the



Cassette and Plenum

Systems shall have the following

'active' area of the ceiling to avoid migration of vapour, or increasing the

extract cassette overhang as a

volume flow. The increase in the extract rate should also reduce the



Grease Producing Equipment Steam Producing Equipment

At Least 500mm Overhang of Equipment At Least 750mm Overhang of Equipment


AFFL (m 2.2 2.5 2.7 2.9 3.1 3.3


FACTOR 1.10 1.00 1.08 1.16 1.24 1.32 1.40

As the finished ventilated ceiling height increases, the extract flow rate shall also be increased. NB The optimum ceiling height for ventilated ceilings should be 2.5m. This ceiling height therefore has a multiple factor of 1.00. As with ceilings above this height, those below require an increase in extract volume because of problems created with potential cross draughts (i.e. 2.2m height = 1.1 factor).


Plenum System

8.6.1 With no proprietary components, the plenum system comprises a series of filter plenum modules which allow

Fig 13 - Plenum Type Ceiling.


DW/1 72 Specification for Kitchen Ventilation Systems the extract air to pass through a single

voids exceeding 1250mm a top cover

or double bank grease filter for contaminant separation before passing

(galvanised steel) shall be fitted at maximum 1250mm above finished

into a plenum box and duct system

ceiling height.

and discharge to atmosphere.

8.7.6 Open builders work plenurns shall not


Supply grilles are integrated into the

be used as any part of an extract

ceiling design to provide make up air comfort ventilation or spot cooling.

system where grease laden air is being

extracted. In these areas, the exhaust

zone shall be top capped. Open 8.6.3 Secure installations are not achievable

builders work plenums may be used for supply air plenums and extract air

with plenum systems.

plenums for steam laden air only.

8.6.4 Grease filters shall be located in

Where open builder work plenums are selected for extract of steam laden air,

accordance with procedures set out in Section 13.


services passing through this void

should be contained within a Supply and Extract Ductwork


The alternatives for removing extract air and supplying intake air should be:

galvanised duct/trunking.


Construction 8.8.1

The material to be used in the manufacture of ventilated ceilings

• via partitioned voids

should typically be 304 grade stainless steel. Some manufacturers incorporate anodized aluminium into

• totally ducted system.

the supporting frame; this form of construction should be agreed with

8.7.2 Where partitioned voids are selected there should be no direct duct/spigot

connection to the extract filters.

Extract should be by means of bellmouths in a sealed plenum

the client or specifier.

8.8.2 The structure that supports the

connected to a ductwork system.

ventilated ceiling shall be adequate for the total weight imposed. As a guide the average installed weight of

Supply air should be introduced via a duct system through bellmouths into the supply void.

both types of ventilated ceiling, ranges between 18kg/rn2 - 25kg/rn2.

8.7.3 For

most efficient operation bellmouths should be not more than


Services, other than ductwork, shall

3m apart in each plenum zone.

not pass through the extract void

Velocities at the face of a bellmouth shall not exceed 3rnls.

where grease laden air is being carried.

8.8.4 Where other services are routed 8.7.4 Where a ducted system is selected it

through voids that carry supply or


dedicated ductwork with coimections to both

steam laden air, access arrangements shall be provided so that adequate and

supply and extract cassettes, via

regular cleaning can be achieved.

plenum boxes.

Steam extract and supply air voids, builders-work partitions, etc. shall be


8.7.5 Where a plenum design is selected open voids above the ceiling shall be sealed. Void depths shall be 200mm minimum to 1250mm maximum. For


painted with an anti-fungicidal, dispersion coating to avoid the collection of airborne dust and dirt particles.

Kitchen Ventilation Systems

DW/1 72 Specification for

barrier being fire rated to a standard determined by the

8.8.5 The ceiling void shall be sealed to the building structure to ensure that an airtight plenum is created in order to avoid any short-circuiting of the air

building owners risk assessment, but with a minimum integrity of 30 minutes and fire stopped.




Where gas services are run through

8.8.10 With both ventilated ceiling options,

the ventilated ceiling void, the installation must comply with

care should be taken if future

modifications to the kitchen layout are

Building Regulations or run within a ventilated sleeve to atmosphere.

considered. It is important to ensure that the provision of extract zoning within the ceiling void is revised to the modified with comply requirements and also that sufficient extract and supply air is available to


mechanical and electrical

services, other than ductwork, shall be

run outside the extract zone, except for electrical services to lights which


shall be fitted with heat resistant

accommodate changes. The guidance of the ventilated ceiling supplier shall

cabling. The services columns shall

be sought prior to modifications

extend through the zone and terminate outside the extract zone.

taking place to ensure the integrity of the system is not compromised.

Installed height of ventilated ceilings

can vary from 2200mm to 3500mm above finished floor level depending upon structural limitations and the



Lighting 8.9.1

Integral lighting may be incorporated into either ventilated ceiling system.

type of appliances being ventilated.

Illumination levels shall follow the

To minimise potential fire risks, it is

Minimum requirement shall be 1P55rated luminaire, achieving an average

recommended that:

• The ventilated ceiling should be cleaned and maintained regularly.

recommendations of Section 14.

of 500 lux at working height throughout the area to be served by the ventilated ceiling. For areas other

than the kitchen refer to CIBSE • All partitions in the ceiling void

should be constructed from

Lighting Codes.

cleanable surface materials that are easy to clean and will not harbour growth of bacteria.

8.9.2 Care should be taken with the

Material thickness of partitioning

lighting should be considered. The

should be at least 0.80mm.

introduction of supply air through the


selection of lighting components as

general lighting as well as task light fitting should be considered to

• Where there is grease producing equipment, the ceiling zone shall

extend the life of the capacitors,

be completely segregated from any adjacent zone by non-combustible imperforate downstands extending

assist in maintaining the cleanliness of

improve illumination efficiency and

the tubes reflectors and diffusers. Emergency lighting shall be to BS

from the structural soffit to the ceiling. This partition shall be manufactured from galvanised

8.9.3 The ventilated ceiling supplier should

steel. The perimeter of each zone

supply photometric data on each

shall be segregated by cavity

project to ensure the optimum

other from barriers any conventional ceiling void with the


luminance levels will be achieved.


DW/1 72 Specification for

Kitchen Ventilation Systems

8.10 Cleaning and Maintenance


For the cleaning and maintenance of ventilated

ceilings see the relevant notes under Section Spigot



The size of the spigots serving both the supply and extract plenums, should be determined by selecting a size appropriate for the air velocity.


The extract spigot area should be determined

by dividing the total extract flow rate by a design velocity of 5-7 mIs. and the supply air volume a velocity of 3-5 mIs.


The width of the spigots should depend on the size and shape of the filter housing, the angle of the filters and whether a wall or island style canopy is used.


The number of spigots shall be determined by

the length and width of the canopy and any restrictions in the ductwork layout but, as a general rule, there should be at least one spigot

for every 3m of canopy to ensure an even air flow.


DW/1 72 Specification for Kitchen Ventilation Systems


10.2.2 For the fabrication of front face discharge grilles, 1 .0mm perforated stainless steel sheet shall be used, the free area selected to suit the design conditions. This arrangement will not provide directional control of the air discharge

Materials 10.1 Stainless Steel 10.1.1 Unless indicated to the contrary in any

particular project specification, all visible surfaces of the canopy and ventilated ceilings shall have the fine

grained finish on view, with all unpolished surfaces concealed.

10.1.2 All polished sheet surfaces shall be protected with a removable, laminated film.

10.3 Insulation 10.3.1 To avoid condensation, canopies that

are provided with a supply plenum shall have all internal surfaces of that

plenum thermally insulated. The insulant shall be a rigid foil faced non fibrous slab, with a class 1 spread of flame.

the offshore and food process

10.3.2 Insulating boards are available in various thicknesses and should be

industries type 316 acid resistant stainless steel should be required

combination of adhesive, tape and

10.1.3 For special canopy applications for

(manufacture reference: EN 10088). Where such specialised stainless steel is necessary, the client shall indicate this requirement from the outset.

fixed to the plenum with a stick pins.

10.3.3 Fibre based insulating materials must not be used in a food environment.

10.1.4 Abbreviations DP2 DPi 2A 2B

= = = =

Dull polished both sides. Dull polished one side. Bright Annealed Descaled or unpolished

TABLE 8- Material Weights (in kg/rn2)_______ 2.0mm or 14g 1.6mm or 16g 1.2mm or 18g 1.0mm or 20g 0.8mm or 22g

Stainless Steel 16.04 kg/rn2 12.87 kg/rn2 10.30 kg/rn2 7.77 kg/rn2 6.40 kg/rn2

10.2 Perforated Sheet 10.2.1 For the diffusion or equalisation of air within the supply plenum of a canopy,

0.8mm perforated sheet should be used.


DW/1 72 Specification for

Kitchen Ventilation Systems


be selected to ensure that no distortion occurs

through either welding or the weight of the panel itself


1 1.3 Fabrication

11.1 General

11.3.1 Cut blanks should be notched and folded into sub sections. These folded

11.1.1 The canopy should be easy to clean, be constructed of non-combustible materials and be located so as not to

joints shall be contained 'inboard' of

the canopy construction to ensure concealment on completion of the

interfere with the cooking process.

final assembly.

sections shall be manufactured in an all-formed, folded and welded construction with joints

11.1.2 Canopy

11.3.2 Consideration should be given to minimise the number of components in which a canopy is delivered to site. This will depend upon both the size of canopy, site access and conditions.

made such that there are no obstructions or obtrusions likely to cause injury or encourage growth of bacteria.

1 1.1.3 All external canopy surfaces should

be vertical to facilitate cleaning, match the ceiling line and maximise the internal collection volume.

11.3.3 Canopies which in length exceed that which can be made from a standard sheet, shall be made in sections which are joined by means of a 20-25mm

wide full height internal flange or

standing seam. After erection, standing seams shall be covered by a

11.1.4 A minimum 50mm x 25mm channel should be formed as an integral part of the valance to provide rigidity to

the exposed edge for the full

full height cover trim to provide a smooth surface to facilitate cleaning.

perimeter of the canopy. Provided that

11.3.4 Canopies that are made using

the air flow rate has been correctly selected, condensation should not

the joint between the sheet and section

extruded section must not be used as

provides a natural harbour for the

form and with the exception of 'condensation' canopies, there will be no requirement for drain plugs.

For ventilated ceiling construction, refer to Section 8.

1 1 .2 Canopies and ventilated ceilings should be fabricated using the material thicknesses shown in Table 9. The material thickness shall

TABLE 9- Sheet Thicknesses Stainless Steel

Valance up to 600mm high Valances over 600mm high Filter Housing Flat Panel Ventilated Ceilings Coffered Ventilated Ceilings Supply plenums Spigots


0.9mm 0.9mm - 1.2mm 0.9mm - 1.2mm 0.9mm - 1.2mm 0.55mm - 1.1mm 0.9mm - 1.2mm 0.7mm

growth of bacteria.

1 1 .4 Sealant 11.4.1 The use of sealant shall be limited to joints or those areas where a hygienic seal is required. The sealant must be of silicon type foodservice quality.

1 1.4.2 For site use, a clear, white or grey sealant should be used for making a seal between the canopy and a tiled wall or ceiling.

11.4.3 Conventional sealant should be used for spigot and ductwork joints.

11.4.4 All products shall be installed in accordance with the manufacturers' recommendations.

DW/1 72 S; ik'atio;: for Kitchen Ventilation Systems




Grease Filtration

12.1 All visible welds shall be ground to a smooth 13.1

A UK standard for the testing of grease filters

surface and reinstated to the finish of the base material by polishing.

has been set by the publication of the Loss Prevention Certification Board's document LPS 1263 - REQUIREMENTS FOR THE

type of disc used for the grinding and


polishing processes may vary according to the grade of material and joint being polished.


The polished areas should be covered with a

should comply with LPS 1263.




low tack vinyl tape to replace the original laminated pvc protection destroyed by the welding.

EXTRACT SYSTEMS. All grease filters used

in commercial kitchen ventilation systems

Filters are used primarily in commercial kitchen extract systems for the removal of flammable grease deposits.

1 2.4

Abrasive discs that have been used on other

materials shall not be used with stainless steel.

The grease extracted by the filters shall be

collected and removed so that it will not accumulate in either the canopy plenum or the ductwork system, or fall back onto the cooking surface. In the event of fire the filter shall also limit the penetration of flame downstream into the canopy plenum. The filter shall be constructed so that there are

no sharp edges or projections and shall be easily removable for regular cleaning.

Primary filters that retain grease within the filtration matrix until cleaned, shall not be used

(not to be confused with those designed with purpose made integral collection reservoirs).

The mesh type filter shall not be suitable except for secondary filtration.

LPS 1263 describes tests to determine both the

grease removal efficiency and the flame resistance of grease filters. The tests are based on procedures that are already in place and are based on the American UL 1046 (F Class) for flame arrestance, and the German VDI 2052 (G Class) for the grease extraction efficiency. The main requirements of the UL1046 test are that;

• There shall be no flame extension of more than 450mm beyond the filter. (MFL)


DW/1 72 Specification for

Kitchen Ventilation Systems

• The filter remains intact throughout the test

• There is no ignition of collected grease on the downstream side of the filter

The results of the VDI test for grease removal efficiency will be:

50% of the smallest particle size will be removed from the air stream.

• No grease falls back onto the cooking surface

This removal will be achieved at plus or minus 20% of the specified airflow.

• No flame exists downstream beyond a time of 120 seconds (DFP)

The required performance of the filter will be based on the results of both tests and to the risk factor of the cooking and building type.

Table 10- Cooking Risks Risk Level

Examples of type of cooking equipment

Boiling with no risks of vapour Conventional frying or processes emitting steady vapour flow Open flame grilling, flame cooking and sudden emissions of hot vapour

Light Medium Heavy

Table 11 - Building Risk Risk Level


Example of type of building in which kitchen is located Small commercial building of single occupancy type Small commercial building of multi-occupancy type Medium size commercial building of single occupancy type

K4 K5 K6 K7

Medium size building of multi-storey Large size commercial building of single occupancy type Large size commercial building of multi-occupancy type Special risks including large shopping complexes and airport terminals

Ki K2

Table 12- Recommended Performance of Filters to comply with LPS 1263


K2 K3 K4 K5 K6 K7

Light GF2O

Risk Assessment (GF Class Required) Cooking Risk Medium GFS2

Heavy GF8O

GF28 GF36 GF44 GF52

GF58 GF64



GF94 GF98







Where the 'G' represents the grease removal efficiency, and 'F'; represents the capacity of the filter to restrict the length of flame.

The designer shall specif' the class of filter required based on the building and cooking risk factors, and it shall be the responsibility of the canopy contractor to provide a filter of the appropriate GF rating. Details of test procedures do not fall within the scope of this document, and further information should be obtained from the Loss Prevention Council.


DW/1 72 SpecijIcatio;i for

Kitchen Ventilation Systems

13.2.1 Grease filters fall into two main 13.4 Mesh Impingement Filters categories; primary and secondary. Typically, most canopies incorporate only primary grease filters and these shall be specified in accordance with

13.4.1 There is no barrier to flame within these filters; therefore mesh filters shall not be used as a primary grease filter.

LPS 1263. Primary grease filters should

be flame retardant and capable of removing as much airborne particulate (i.e. grease, oil etc) from the air stream as possible, to maximise the filtration process within the canopy. Secondary mesh type impingement filters can be incorporated to the rear of the primary filters providing they do not affect the


Baffle Filters

13.5.1 Baffle filters comprise a number of

interlocking vanes which when assembled form a two-pass grease removal device. The pressure drop

fire arrestance criteria as required by

remains constant and the blades provide a barrier in the event of a

LPS 1263. Inclusion of secondary

flash fire. Baffle filters should be

mesh type impingement filters shall not reduce the LPS 1263 requirement for the primary grease filter.

fabricated entirely from stainless

13.2.2 The use of secondary filters,


13.5.2 The grease laden air passes through the filter and by a series of forced

sometimes referred to as coalescers, serves to encourage airborne gases to condense on the surfaces and thereby

changes in direction and velocity, the

substantially reduce the moisture

vanes. The deposited grease is then

content of the air being extracted.

drained off through a number of weep

grease becomes separated in the air stream and is deposited on the vertical

holes spaced at adequate intervals into a collection drawer which shall

13.2.3 Disposable panel type filters shall not be used for grease extraction. Where

be regularly cleaned.

high levels of contaminant are produced, then higher degrees of grease separation can be achieved by

the use of cartridge, water wash or water mist systems.



of type of grease filter currently

13.5.3 The capacity of the collection drawer shall be sufficient to suit the type of cooking and frequency of cleaning and because the grease is retained, care shall be taken to ensure that the grease collection drawer is isolated

available and their main properties are shown

from the extract air stream as

in Table 13.

illustrated in figure 14 to prevent reentrainment. '3. 1. CONTAMINATED AIR 2. GREASE SEPARATION



Fig 14— TypicalAirfiow Through Filter Housing

DW/1 72 Specification for Kitchen Ventilation Systems

13.5.4 For plenums that contain more than one filter, supports may be required to

ensure that the housing remains stable.


shall be easily

removable and installed so as to minimise air leakage around the perimeter.

13.5.5 Where installations are

being refurbished, baffle filters shall not be installed in a plenum previously used with mesh filters unless a collection

manual system where the operator pushes a start and stop button at the beginning and end of the cooking process each day. Automatic systems

are also available which allow the control of a set number of systems with pre-set sequencing of water cycles, and automatic starting and stopping.

drawer and grease run is added and the plenum is revised to avoid reAny increase in entrainment.

13.8.3 Cleaning is achieved by spraying the

resistance shall be taken into account

work pipe system, integral automatically injecting the plenum

when selecting a new fan or considering the adequacy of the existing one.


13.8.2 Water-wash canopies are operated by a control panel. The basic panel is a

interior of the canopy extract chamber

with pressurised hot water via an

with a predetermined amount of detergent. The waste water flows from the system through a plumbed drain.

Baffle filters shall be installed at an angle of

not less than 45 deg from the horizontal.

1 3.7 Cartridge Filters

13.8.4 The wash cycle is generally activated for between 2 and 3 minutes at the end of the day after the cooking equipment and fans have been turned off.

13.7.1 Cartridges filters comprise a high velocity slot opening onto a series of 13.9 Continuous Cold Water Mist baffles which cause multiple direction 13.9.1 Tn addition to the water wash system a changes to the air flow. cold water mist can be incorporated to enhance grease extraction. The water 13.7.2 Available in a combination of size and length to suit the air flow, cartridge mist system runs continuously during filters shall be installed over the full the cooking operation. The vapour length of the extract plenum, with an entering the canopy passes through the mist which causes the grease integrally designed slope to allow the trapped grease to fall through a drain particles in suspension to drop in temperature, solidify, increase in size to a grease drawer. and drop to a drainage trough from which it is flushed to a drain. 13.7.3 Should be for used with moderate to heavy grease load applications.

13.9.2 The mist system has an additional

13.8 Water Wash

advantage in that the continuous flow of cold water cools both the canopy

13.8.1 The water-wash system comprises an extract plenum similar to the one used

and the exhaust air, is particularly suitable for solid fuel appliances

with cartridge filters, but also

where the mist will also extinguish hot embers that may be drawn up into the canopy.

incorporates an inbuilt self cleaning system that has the dual function of catering for routine maintenance as well as providing fire protection to the plenum and duct.

13.10 The bacterium legionella occurs naturally in water sources and, when in sufficient numbers,

can cause 'legionnaires disease' by the inhalation of water laden air in an aerosol form


DW/1 72 'iiti for Kitchen Ventilation Systems • CIBSE

Technical Memorandum: Minimising the risk of legionnaires disease

by susceptible individuals. This is unlikely to occur with water wash and water mist systems

due to the fact that the water supply to the

(TM13: 1991)

system is constantly changing and the

• The Institute of Plumbing publication "Legionnaires' Disease - Good Practice

confined nature of the spray. If it is thought that there is cause for concern, then further

Guide for Plumbers"

guidance must be obtained from either:

• HSC document - "The prevention and

13.1 1 Typical wash plenums are illustrated in fig

control of legionellosis - Approved Code of Practice L8"


Fig 15 - lvpical Water Wash Plenums.

Table 13- Types of Canopy Grease Filter and Their Main Properties Type

Recommended Face Velocity




4.5 - 5.5 mIs (at slot)

Inexpensive Non - over Loading_pressure drop

Higher pressure drop than mesh filters


4.0 - 5.5 mIs (at entry)

Higher efficiency Non overloading pressure drop

Higher pressure drop than baffle filters Special plenum fabrication required

Water Wash

4.0 - 5.5 mIs

Higher efficiency Non overloading Low maintenance

Expensive. Very high

Very efficient. Low maintenance. Non overloading

Expensive. Very high pressure drop Hot and cold water supplies and drains

(at entry)

Cold Water

4.0 - 5.5 m/s (at entry)

pressure drop. Hot water supply and drains required.

required For types and properties of ventilated ceiling filters, refer to Section 8


DW/1 72 Speciflcatioii for

Kitchen Ventilation Systems


14.7 The light housing should be designed with

Canopy Lighting

14.8 Wiring from the light fittings to any junction

14.1 Lighting in a kitchen canopy should provide an average illumination level of approximately 500 lux at the working surface and standard

adequate ventilation, especially at either end.

point on the canopy must be heat resistant and

installed in a low smoke and fume (LSF) material. The power supply should be part of the electrical services contract.

fluorescent type fittings, installed at a height of

1200mm above the cooking surface should 14.9 The light housing shall be manufactured from a material or colour which will ensure fulfil this requirement. In comparison with maximum light reflection downwards towards other systems of lighting, the fluorescent

fitting is generally the most efficient and

economical option with the best life expectancy. They should be incorporated into

a suitable housing to isolate them from the cooking process. See CIBSE Code for Lighting, Lighting at Work, BS ISO 8995 and BS EN 12464- 1.



the working surface.

14.10 The following formulae should be used to determine the level of illumination achieved when details of the lighting components are known. 14.10.1 The level of illumination in lux should

be calculated as follows

lighting housing should be recessed into

the canopy to provide an easily cleanable

No. of tubes x average tube life x ufx mf canopy area

surface devoid of unnecessary, inaccessible

joints and seams. Where surface mounted canopy lights are unavoidable, then smooth surfaces and good 'clean-down' properties

14.1O.2The number of fittings required should be calculated as follows

should be provided.

Canopy area x required level of illumination average tube life x ufx mf

14.3 The light enclosure shall be sealed against the ingress of grease and moisture. Surfaces facing the cooking area shall be designed to achieve a rating of 1P55 - see appendix C for details of IP ratings.

14.4 All sealing gaskets between the removable reflector and the light housing shall be of food

quality neoprene and be able to withstand temperatures up to 100 deg C.

The inclusion of double tube fittings does not necessarily double the level of illumination. A

factor of 1.5 times higher should be used to give the correct level of illumination when using double tube fittings.

14.10.3 Where mf= maintenance factor = 0.70 uf= utilisation factor = 0.38

and average tube life is given in

14.5 The lighting lens shall be made from a temperature resistant material such as polycarbonate sheet or safety glass. In both cases, the outer surface should be of a smooth and easy to clean finish. Care shall be taken to ensure that where polycarbonate sheet is used it

shall be capable of withstanding the temperatures generated by the cooking processes.

14.6 The light housing shall have an easily removable cover for easy access and replacement of the fluorescent tubes.


Table 14.

TABLE 14- Average Tube Life Tube Length

600mm 1200mm 1500mm 1800mm

Output 18 Watt 36 Watt 58 Watt 70 Watt

Average Life

1100 hours 2800 hours 4550 hours 5600 hours


DW/1 72 Specification for Kitchen Ventilation Systems are based on supplied by manufacturers of 'warm white' tubes.

14.10.4These figures information

Should alternative products be selected, then different factors may apply.

14.10.5 Where standard light tubes are used, these shall be encapsulated within a

protective sheath to render them shatterproof.

14.10.6 Natural deterioration in illumination

occurs to all fluorescent tubes. Annual replacement should ensure the original lighting level is maintained. 14.10.7 The CIBSE Code for Lighting shall be complied with (see Appendix F).

14.1 1 Where surface mounted lighting is to be used all electrical wiring shall be concealed above the canopy.

14.1 2 Alternative positions for the location of light fittings are shown in fig 16.

SECTION 15 Ductwork 1 5.1

The correct standard of ductwork selected to complete the installation is as important as the selection of the canopies themselves.

15.2 For the distribution of supply air to the canopy, the ductwork has no special requirements other

than the application of thermal insulation where the supply air is tempered and the installation at a minimum F6 filtration level for the incoming air. Bird mesh screens to the rear

of any inlet louvre shall be incorporated. Insect mesh shall not be used as it can become easily blocked.

15.3 Under normal circ*mstances and providing it

runs within the fire compartment of the kitchen itself, extract ductwork shall also have no special requirements.

15.4 All ductwork as described in 15.2 and 15.3 shall be low pressure Class A and be in accordance with HVCA Specification number DW/144 with a minimum thickness of 0.8mm.

15.5 Where it is not possible to immediately discharge the captured air within the confines

of the kitchen fire zone, fire rated ductwork must be used to comply with BS 3476 part FLUORESCENT IN ROOF

24/B S 5588 part 9. For further information see Appendix D.

1 5.6 Where total 'grease tightness' is required within the kitchen fire zone, all ductwork within the kitchen compartment and not discharging directly to atmosphere shall be constructed from either 1.2mm stainless steel

or 1.6mm zintec, be of fully welded FLUORESCENT IN SUPPLY PLENUM


construction with welded angle iron flanges and use full faced gaskets. Gaskets shall be non porous, impervious to grease and cooking oils and capable of withstanding the higher temperatures experienced in kitchen extract systems. Mild steel ductwork should also be painted externally with 2 coats of protective paint before leaving the manufacturers works.

15.7 Where a waterwash or watermist type filtration Fig 16 - Location of Lighting.

system is used, horizontal ductwork shall slope back to the canopy with a fall of 1:50.

— 35

DW/1 72 Specification for Kitchen Ventilation Systems

15.8 Grease filters do not remove all of the airborne grease produced therefore care should be taken against staining the fabric of the building at the discharge point.


Particular attention shall be paid to the design

15.11 When designing kitchen supply and extract systems the duct velocities shown in Table 15 shall be followed.

Table 15- Duct Velocities

of ductwork to extract steam from dishwasher and pot washing machines due to the very high

level of humidity present. With the risk of condensation, the following precautions shall be considered to prevent leakage through the duct joints.

Main Runs Branch Runs Spigots

Supply 6-8 mIs 4-6 mIs 3-5 mIs

Extract 6-9 rn/s

5-7 rn/s 5-7 rn/s

15.12 All interior surfaces of the ductwork shall be joints in the direction of the flow of accessible for cleaning and inspection

• Use of stainless steel ductwork with slip condensation.

purposes. In the absence of a detailed cleaning

specification/method, access doors shall be installed at 3m centres. The panels shall be of at least the same thickness material as the ductwork, be grease tight using a heat-proof gasket and contain minimum projections into

• Ductwork installed with a fall back to the machine.

• Apply external thermal insulation to

the duct. For recommended cleaning

minimise the condensation.

procedures refer to section 25 and the HVCA publication TR/1 9 - "Guide to Good Practice -

• Ensure that longitudinal joints are not on the bottom of the ductwork.


• Site-weld cross joints on stainless steel ductwork, particularly across the bottom

of Ventilation Systems" (see

Appendix F).


On horizontal duct runs, access doors should

be installed on the side of the duct, with the

and for 50mm up each side.

underside of the door at least 40mm above the

underside of the duct. On vertical ducts,

• Ensure that cleaning doors are not on the underside of the ductwork.

cleaning doors shall be provided at each floor level.

• Consider the use of all-welded plastic ductwork.


15.14 Discharge points shall be positioned such that the extracted air cannot be entrained into a

No system shall be connected into the kitchen

supply system. The ductwork shall discharge

extract system where the route selected does

at least I .Om above any openable window.

not minimise the number of changes in direction and possible grease traps. Where ducts from more than one canopy are joined together, then branch cormections should be


The discharge terminal shall be open without

mesh and designed to achieve an exhaust or efflux velocity of 12-15 mIs or as required by

flush on the underside.

the Local Authority from whom approval shall be sought. However, consideration should be

Internal thermal or acoustic lining should not be used, and turning vanes should be avoided wherever possible.

given to situations where the lack of a mesh/guard might allow hand access to operating fan blades.

Where it is not possible to immediately 15.16 All exterior ductwork should be supported discharge the captured air within the kitchen fire compartment, fire rated ductwork shall be required. For further information see Appendix D.


with fixings that do not penetrate the duct wall. Where this is not possible, the duct wall shall be made good with sealant and steel washers.

DW/1 72 Specificat;ii for Kitchen Ventilation Systems

15.17 The use of a 'chinaman's hat' type of cowl 15.18 Drains shall be installed at the base of all risers

should not be used due to the potential

(see Fig 17).

downdraught caused and the risk of re-entry of

the extract air back into the building. Alternative types of discharge terminal are shown in fig 17 and 18.

Fig 17- Drain

300 MAX

15 rn/s





Fig 18- Alternative Terminals without internal drains





Fig 19- Alternative Terminals with internal drains


DW/1 72 Specification for Kitchen Ventilation Systems


finishes to be applied such as tiles or plastic facings. It shall also be established whether

the canopy is to be installed prior to these

Installation 16.1

To ensure the smooth running of an installation, the following items shall be established at an early stage of the contract.

16.2 Canopies and ventilated ceilings are usually a second fix item. The installation should be programmed to follow completion of the mechanical services first fix, but before either

the cooking equipment or false ceilings are installed.

finishes. If the canopy is to be installed first then dimensional tolerances shall be agreed with the main contractor. Where a canopy is recessed between two walls then a finished

dimension needs to be established before manufacture is started. Ventilated ceilings are

usually installed after the wall finishes are complete. As such the finish should extend to at least 50mm above the installed height of the

ventilated ceiling. The provision of ceiling trims will then be undertaken by the ventilated ceiling contractor, with care exercised to avoid

breaching the air-tight integrity of the

16.3 Because of the many canopy sizes, access routes should be established to ensure that components can be easily manoeuvred into the

building at the appropriate stage of

ventilated ceiling system.

16.8 Canopies are fabricated to specific geometric shapes

and dimensions. During the

construction. Consideration shall be given by

installation, inaccuracies in the building

all parties to special access or lifting provisions that may be required.

installations the canopy supplier should

16.4 The canopy clearance from the finished floor level to its underside is usually set at 2000 2100mm. If alternative levels are required, they

shall be stipulated prior to the production of the manufacturing drawings.

16.5 Canopies and ventilated ceilings are usually installed before the catering equipment which

structure may be highlighted. For complex provide templates prior to the delivery of the canopy.

16.9 Protective finishes such as vinyl film, impacttype wrapping, protective boarding and tape shall be left in place until the final cleaning programme. The canopy and ventilated ceiling contractor would not normally be expected to

return at later date to undertake this work

can make setting out points difficult to

unless specifically instructed to do so at tender

establish. Pre-determined datum points agreed


formally with the catering equipment 16.10 For canopies, the provision of ceiling trims installation contractor should ensure that the canopy or ventilated ceiling can be suspended precisely over the intended equipment position and in line with service distribution units.

16.6 The

ventilated ceiling manufacturer should be advised at an early stage on the type of fixings to be used and whether any secondary support provisions are required. Various suspension methods may be used, but the number of fixing points shall be selected to carry the weight, maintain both the shape, integrity of the finished installation and canopy


include provision to overcome any site discrepancies.

16.7 The





manufacturer shall be advised of any wall 38

will normally be undertaken by the false ceiling contractor. Care should exercised when

fastening trims to a canopy to avoid fixings penetrating the canopy skin. Even greater care shall be taken on waterwash canopies to avoid breaching the watertight integrity. Ventilated ceiling installers should fit wall trims and site measure infill pieces to tie in to their system.

16.1 1 Prior to leaving site the canopy and ventilated ceiling installer shall arrange for the canopy / ventilated ceiling to be inspected by the client

to ensure that the installation has been completed to his satisfaction.

16.12 The supplier

shall ensure that the canopy/ventilated ceiling performance rating plate has been fitted.

DW/1 72 Specification for

SECTION 17 Fans 17.1

Care shall always be taken with the location of the supply and extract fans to ensure that there

is sufficient space for regular cleaning and maintenance. Limited space shall not restrict selection of the correct fan.

1 7.2 Kitchen ventilation systems have relatively high resistances against which a fan has to operate. The fan should be selected to handle the design resistance with up to an additional 10% pressure margin allowed to suit possible

extensions to the original kitchen plan. Regulation of the air flow should be achieved by either variable speed control if the selected

fan is suitable, or by the use of balancing dampers.

17.3 Backward curved centrifugal, mixed flow or axial flow impellers are preferred as they are less prone to unbalance and are more easily

maintained and cleaned due to their open

construction. Fixed or adjustable metal impellers with a robust and open construction

shall be used, as lightweight multi-vane or plastic-type impellers can warp and are prone to collecting concentrations of grease. Plastic

bladed fans can however be used where the canopy extracts non-grease producing, low temperature fumes.

17.4 Conditions within the kitchen in which the fan has to operate are normally between 40 and 60 degC at 95% relative humidity. Most motors are rated to 1P55 and are capable of operating within these conditions without the necessity to mount the motor out of the airstream.

1 7.5 For fans that have the motor within the airstream and are ventilating from cooking equipment that produces higher levels of temperature and humidity indicated in 17.4, then the specification for the motor shall be

upgraded to

withstand more onerous


17.6 An audible andlor visual indicator should be included to warn of fan failure. This should to operate on pressure difference rather than air

Kitchen Ventilation Systems

movement because of the possibility of grease build-up on the vanes.

17.7 The provision of drain holes at the lowest point of the motor to allow condensation to drain freely is recommended, these shall be of the porous type to avoid downgrading the Index of Protection (IP) of the motor.

1 7.8 Both variable and two speed regulation are now common features, but it is essential that when grease is being produced, the system shall operate at its design duty. A minimum extract level shall be set within the regulator to ensure that, even when set at low speeds, an acceptable ventilation rate is maintained as reduced speeds may cause the carry-over of

grease through the filter. This facility is a

standard feature of the controller with proprietary speed regulators.

1 7.9 Where a make-up air system is selected, the speed regulators for both the supply and extract fans shall be electrically interlocked to ensure that the desired balance is maintained.

17.10 BS 6173 states that an interlock of the ventilation system to the gas supply serving the cooking equipment shall be installed so that, in

the event of air flow failure, the gas supply is

switched off. The supply fan shall also be isolated when a fire suppression system is activated in fire mode. This will involve the fitting of an automatic solenoid valve in the gas supply pipe work and an airflow-sensing device such as a pressure switch, vane switch

or torque switch. The inclusion of this interlock is a requirement for all new powered

extract systems. For existing installations where cooking equipment replacement is like for like, no action is required. However, the contractor shall quote for the inclusion at all

times; failure to do so could lead to legal issues. If an existing kitchen has any form of upgrade, then the contractor shall quote for the inclusion. The Client's insurance company may have a requirement that this work is done; this may reduce the premium paid.

17.1 1 Fans selected for use with dishwasher systems shall be fitted with 'tropicalised' motors that

are capable of operating in the saturated atmosphere, or a fan with a motor out of the


DW/1 72 Specification for

Kitchen Ventilation Systems

airstream. The fan should be electrically linked

of the flumes being exhausted. Table 16 lists materials with the maximum temperatures at

to start with the washer and include an automatic run-on timer to disperse residual moisture as the system cools down. Another option is to specify anti-condensation heaters for larger motors, or for smaller motors to connect a single phase 24 volt supply to a winding when the motor is idle to provide a little heat and thus prevent condensation buildup.


Flexible connections shall be suitable for use

with a grease laden atmosphere, positively fixed by clamps or bonding to prevent air leakage. Under fire conditions the material must have a minimum integrity of at least 15

which they are suitable for continuous operation:

Table 16: Flexible Connections Temperature Ratings Fire retardant PVC coated nylon 40°C Loaded PVC coated glass fibre (acoustic) 40°C 120°C Neoprene coated glass cloth Aluminised glass cloth 150°C Silicon coated glass cloth 2O0°


minutes and be selected to suit the temperature

The following table compares the advantages

and disadvantages of the various types of fan.

Table 17: Types of Fan FAN TYPES


1. Centrifugal 1) Large range of pressure and volume Fan Sets characteristics 2) No temperature limitations 3) Robust and easily maintained 4) Adaptable changes in system requirements with pulley/motor changes


1) An expensive option

2) Requires more space than is usually available in the kitchen

3) Requires regular maintenance to check drive belt wear unless direct driven fans are used 4) Forward curved fans should only be used for supply systems

5) Standby motors can be more readily fitted 2. Bifurcated Fans

1) Robust with no temperature limitations

1) Less expensive than the centrifugal fan but not a cheap option

2) With motor out of air stream this fan is still considered one of the safest options with high temperatures

2) Heavy in construction and therefore not always easy to support

3) Easily installed into a ductwork system

3) This fan is best situated within a plantroom since on large duties, the fan can be bulky in size and too noisy for siting within a working environment

4) Robust and easily maintained 4) In-duct noise - will probably require attenuation

5) Restricted range of resistance capability

6) Standard unit not readily available with speed regulation. 40

DW/1 72 Specification for Kitchen Ventilation Systems

Table 17: Types of Fan FAN TYPES



3. Belt Driven Axial Fans

1) Compact with an extensive duty range especially when operating in contra-rotation.

1) This fan needs regular maintenance - in hot environments the drive belts are likely to fail more regularly (visual or audible alarm for fan failure is an option)

2) Few temp limitations

3) Easily installed into a ductwork system

2) Not as robust as the above fans but suitable for most kitchen applications

4) A less expensive option 4. Axial Fans (Metal Impellers)

1) Compact with an extensive duty range especially when operating in series

1) High temperature limitations but will serve for most general kitchen vent systems

2) Easily removed for maintenance and cleaning

2) Not as robust as items 1 and 2 but still suitable for most kitchen applications

3) A cheaper option than the above unless dual fans are necessary

5. 'In-Line' Centrifugal and Mixed Flow Impellers

6. Roof Extract Fans (Vertical Jet Discharge with Centrifugal Impellers)

1) Compact with a good duty range which can serve many kitchen vent systems

1) High temperature limitations but will generally serve the majority of kitchen systems

2) Generally less expensive than the above options.

2) Not as robust as items 1 and 2 but still suitable for most kitchen applications

3) Easily removed for maintenance and cleaning

3) Forward curved fans should only be used for supply systems

1) Compact and, where the motor is encased outside the air stream, has a good temperature range

1) High temperature limitations but will generally serve the majority of kitchen vent systems

2) Easily removed for maintenance and cleaning

2) With poor roof access this type of fan can be a problem to maintain

3) No space restrictions

4) Good external appearance

3) More expensive than in-line/axial fans but dispenses with necessity of discharge ductwork


DW/1 72 Speciflcation for Kitchen Ventilation Systems





18.1 Kitchen extract systems usually operate at

19.1 Volume control dampers are often necessary

sensitive times such as early in the morning

but should be kept to a minimum and

and late at night, so the amount of noise

incorporate the following features:

generated shall be kept to a minimum. The level of noise and vibration from the plant shall not be transmitted through either the structure

• For extract systems, the damper blades shall be fabricated from stainless steel.

of the building or the ductwork so as to be a

nuisance for those either working in the

• The operating mechanism shall be outside

the airstream and be capable of

conditioned space, or in adjoining premises.



withstanding the higher air temperatures

average human cannot distinguish

associated with kitchen extract systems.

between two sound pressure levels up to 2dB

apart. Above this level there a perceptible increase in the overall level of noise. Acoustic equipment shall therefore be selected to limit the increase in level to 2dB above ambient.



19.2 If a fire suppression system is incorporated within the system and a volume control damper is used in an extract spigot, then the duct protection nozzle shall be downstream of the damper.

of noise levels is subjective, but

within the conditioned space a level between

NR4O and NR5O would normally be

19.3 In accordance with BS 5588, fire

dampers shall not be used in the extract system from a

acceptable. The atmospheric side of any

kitchen as the fire authorities may use the

system requires individual examination but Local Authorities will usually advise on their specific noise requirements. Local Authorities usually refer to BS 4142 - "Rating of Industrial

extract fan to clear smoke from the kitchen.


When fire dampers are required on the supply

side, the following points should be

Noise Affecting Mixed Residential and


Industrial Areas" as the basis of their criteria. Generally, the maximum acceptable noise level

• The damper shall be of a robust

at the discharge point of the system is that

construction suitable for its application and

which should not increase the overall level by more than 2dB(A). This is difficult to achieve

be complete with an installation frame where appropriate.

in residential areas and wherever possible, vertical discharge of ducts, slower running fans and lower duct discharge velocities should be

• A visual or audible alarm to signal damper

closure should be considered if the fire

selected. Where this is not possible, then in-

damper is in a remote location.

line attenuators shall be installed.


Where in-line attenuators are used, they shall


be constructed so that there is no grease impregnation into the acoustic media. A protective membrane shall be specified for this

purpose, this will reduce the design 19.6 performance of the attenuator. This should be taken into account when selection is made.


Isolation of vibration using correctly specified resilient mountings or pads, together with heat re sistant flexible connections to the ductwork should

ensure minimum transmission to the structure.


Back-draught dampers should not be used as

they are difficult to clean and prevent a natural

'stack' effect from the kitchen which would otherwise release overnight lingering smells. For Ventilated Ceilings volume control

dampers shall be installed either in the dedicated ductwork or on the plenum boxes.

DW/1 72 Specification for Kitchen Ventilation Systems


20.5 Suppression may be achieved by using carbon dioxide, chemicals or water. Carbon dioxide is not generally used due to the high initial cost and the lack of cooling capability.

Fire Suppression 20.1

The significant presence of flammable grease

and related particles contained within kitchen extract systems, combined with the possibility

of fire ignition caused by the cooking equipment, creates a hazard level above that

which is normally encountered in other ventilation systems.



ventilation systems exhaust grease

laden air and vapour mixtures from a kitchen, the design must provide a level of protection to

ensure the well being of occupants and fire fighting personnel, and limit the damage to the property and cooking equipment.




Chemical Systems

20.6.1 Almost all

fire suppression or

extinguishing systems use special

chemical agents which provide protection to the kitchen canopy. Chemically based systems can be in a liquid or dry agent form, but the liquid type is preferable as a greater level of

cooling to the seat of the fire is provided and post activation clean-up time is much quicker.

206.2 These systems are activated either

Whilst the correct maintenance and use of

manually or automatically in the event of a fire. Thermal fusible links, which

cooking appliances and ventilation systems will help prevent potential fires, it is equally

temperatures, are strategically located

important that in the event of a fire it is

in the extract air path above the

immediately detected and extinguished and

cooking equipment to be protected.

can be calibrated for varying

prevented from spreading to other areas of the building.

20.6.3 When the fire suppression system is

a surface fire suppression system is

as gas or electricity serving the appliances, must immediately be


specified, manufacturers instructions shall be

followed. See Fig 20 for a typical system layout.

activated, mains energy supplies such automatically shut off and isolated.

20.6.4 The chemical agent stored within the






Fig 20 - Fire Suppression Schematic


DW/1 72 Specification for

Kitchen Ventilation Systems

system is released along

the distribution pipework and discharged at high velocity through spray nozzles

equipment requiring protection and whether extraction is by means of a canopy or ventilated ceiling. In all cases, the relevant manufacturer's recommendations shall be strictly

toward the appliances that require protection. When the extinguishing agent comes into contact with hot

followed as they will advise on nozzle requirements and if single or multiple systems are needed.

greasy surfaces foam is formed which

suppresses the combustible vapours and prevents the fire restarting. This

20.8.2 The following are typical grease producing appliances requiring protection, but it is good practice to

process is called saponification.

20.6.5 Some systems can also be activated

seek the advice of the fire suppression system manufacturer or installer.

manually by remote located pull stations normally positioned adjacent to exit doors along escape routes. This

may be the requirement of the local

• Fat fryer, fat cooker

fire officer or design engineer.


• Griddle Water Systems

• Salamander and chargrill 20.7.1 The principle of this system is almost identical to the chemical type with the same design philosophy, installation characteristics, mains shut off action and alarm status. However, the system

• Oven ranges

• Bratt pans

can only be used where there is a

• Pizza ovens

sprinkler main available.

• Char broiler 20.7.2 Special 'sprinkler' style nozzles with suitable temperature ratings supplied with water directly from the main sprinkler storage system are used to

• Chinese Wok Ranges

• Mesquite Grill

spray a fine water mist discharge onto

• Rotisserie

the cooking appliances. This system has the advantage of a plentiful supply

of water and less 'down-time' after a

fire as only the area where the fire occurs is sprayed, whereas with a chemical system, the whole canopy is flooded.

• Open Tandoori


Installation Considerations

20.9.1 A layout drawing of the proposed

system shall be provided for co-

20.7.3 The water spray performs a dual function when fighting a fire. The sprayed mist first absorbs the heat generated and becomes steam. This in




contractor, who is also capable of

hence starves the fire of the oxygen

preparing the design and obtaining his equipment from a single source shall

System Design

20.8.1 The

size and extent of a fire

suppression system will depend on the type of kitchen in question, the type of


20.9.2 An

turn displaces the air locally and necessary for combustion.


ordination purposes and used during the installation works.

be appointed. All work shall be carried out in accordance with the technical manuals of the equipment manufacturer/supplier to ensure that warranties are not invalidated.

DW/172 Se'i,'tr:r: for Kitchen Ventilation Systems 20.9.3 For successful and correct operation, the internal temperature shall not fall below 0 degC or rise above 54 deg C.

20.11.2 Good housekeeping shall be practised

20.9.4 Chemical fire suppressant is an alkaline compound, all due care and

• Keep the hazard area clean

attention must be taken when handling such a substance. Contact with eyes and skin must be avoided and COSHH Regulations complied with.

and the following check list is suggested as a general guide:

• Flammable and corrosive cleaners must be avoided.

• The kitchen exhaust ventilation system should always be running when the kitchen is in use.

20.10 Testing and Commissioning • Grease Filters should always be in 20.10.1 Once the system has been completely installed it shall be commissioned and

place when the ventilation systems

tested in accordance with the

build up in the ductwork and

manufacturer's recommendations.

restrict the spread of flame into the ductwork.

20.1O.2There is normally a requirement to test the release assembly mechanism before the gas cartridges are installed. Also individual components like pull stations, mechanically or electrically activated valves, electrical switches,

pressure switches and the detection

are running to minimise grease

• System efficiency should always be maintained by regular monitoring.

• System tampering should be avoided

system shall be fault tested in-situ.

• Regular visual checks on the

20.10.3Once the system testing and commissioning process is complete,

whole system undertaken by the owner/kitchen head

acceptance certificates for the

installation shall be completed for approval and signature. The customer

or end user is then in a position to

• For further information refer to the ABI/BSRJA document, "Fire Risk Assessment for Catering Extract".

arrange financial cover with a recognised insurance company against loss or serious damage to the kitchen or the building as a whole. 20.1 1 Maintenance 20.11.1 Following handover of the system, it

is recommended that a 12 month maintenance contract with the fire suppression installation contractor is entered into. The agreement should normally include 12 month guarantee for provision of spare parts required and labour against any installation or

manufacturing fault. Subsequent maintenance should be required at regular six-monthly intervals with

major system overhaul every 3 years maximum. 45

DW/1 72 Specification for Kitchen Ventilation Systems

SECTION 21 Service Distribution Units 21.1 Service distribution units are purpose made self-supporting stainless steel enclosures designed to house the various piped and electrical services between the point at which

they enter the kitchen and the cooking appliance. (see Fig 21) They are increasingly

specified as part of the 'canopy ventilation' package to ensure that interface problems are

kept to a minimum, especially where the vertical columns connect to the underside of the grease tight extract housing. Ventilated ceilings shall be co-ordinated with vertical columns in order to minimise the loss of active extract filters.

21 .4 For columns containing gas services a ventilation grille is required at high and low level.

21 .5 Controls for the fire suppression system are normally housed within the electrical column and if a water-wash system is fitted, then the

control panel should be housed within the pipework riser.

21.6 The horizontal raceway or spine running between the columns is the section of the distribution unit from which the connections to

the cooking equipment are made. To prevent damage from mobile catering equipment a

'bumper' rail should be considered, which should be either be fabricated in stainless steel or preferably supplied in rubber.

21.7 The units, which can be either wall-mounted or

21 .2 Each element shall be sized to suit the

island type, provide for single point

particular services being used in the kitchen, to ensure compatibility and be totally integrated with the installed canopy.

allocated to allow for future expansion and

21.3 Each unit normally comprises two columns, one to house the electrical works and one to

connections for all site services. Space can be

access is provided to the interior of the distribution unit by either hinged or removable panels with quick release fixings.

provide the piped services such as hot and cold 21 .8 All pipework connections between the spine and the cooking equipment should be made by water, drinking water, steam, condense, waste, using quick-release or proprietary connections. gas and compressed air. The vertical column It is essential that integral services are carried should have adjustable plinths to accommodate out by competent tradesmen and in accordance uneven or sloping floor finishes. with the relevant codes of practice.

Fig 21 - Typical Services Distribution Unit


DW/1 72 Specification for Kitchen Ventilation Systems

21 .9 Mains isolators, circuit breakers, sockets, plugs and internal wiring can all be fitted at minimise manufacturer's works to coordination problems at site. Combined gas and electricity 'knock-off' buttons shall be

SECTION 22 Odour Control

provided on the end of each vertical column.

22.1 Odour pollution problems are particularly difficult to solve, as the level of odour 21 .10 When the integral services are factory fitted, produced can vary dependant upon the then the supplier shall be responsible for cooking process involved, such as the cooking testing and certification and for the provision of earth bonding.

cycle, the position of the discharge and the wind speed and direction. All systems should

21 .1 1 Service distribution units can be supplied as a

simple stainless steel housing for the installation of plumbing, electrical, and fire protection services by others or as a fully fitted


be offered therefore on the basis of odour reduction rather than elimination. Whilst conventional systems should normally

discharge at least im above roof eaves level,

pre-fabricated system complete with all

with an effective odour control system

mechanical and electrical services.

installed, it should be possible discharge to be made at a low level.


for the

When low level discharge is considered, the

following shall be taken into consideration:

• Whether the discharge is into confined areas such as courtyards.

• Whether it is positioned too close to air intake systems.

• The discharge velocity. • The height above external ground level. • Approval has been obtained from the Local

Authority to comply with Building Regultaions.


Molecules of cooking odours are generated by

the combustion of animal and vegetable matter

which results in a particulate and gaseous mixture. The particulate phase comprises small food deposits and hydrocarbons or smoke, the concentration level of which will vary with the type of cooking. Whilst smoke can be reduced by removing the particulate, it is the gaseous or

vapour phase which contains the odour and therefore needs to be treated.


These molecules are too small to be removed

by filtration alone, the solution is found by selecting a combination of equipment from the

following options, the extent of which will vary according to the problem.


DW/1 72 Specification for

Kitchen Ventilation Systems

• A basic filtration unit for use with low

sought before carbon filters are used in any kitchen extract system.

odour problems may be supplied containing three stages of progressively more efficient filters. Disposable pleated filters precede a 95% efficient bag filter, followed by a 99%

efficient absolute filter. This system will

• As an alternative to using activated carbon, odour absorbing granular chemicals such as potassium permanganate or metal iron salts

not deal with the gaseous phase but is

may be used. The chemical oxidises the

intended to reduce the visible particulate,

odorous gases into a solid form and retains

i.e.smoke, to a maximum level of 0.3

them. However, compliance with Local Authority regulations shall be ensured

microns and all components should to be

monitored closely and replaced when

before the use of these systems, as they are prone to the same limitations that exist with activated carbon.

required. This system should only be used where a high efficiency canopy filtration has been installed such as water wash or mist system.

• Providing staged pre-filters are installed, odour neutralising liquid spray systems can be injected upstream of the extract fan. The cooking odours are neutralised by starving the odour molecules of oxygen. This makes a recirculation system possible for electric cooking equipment whereby, after passing

• An alternative to the 3-stage disposable

filtration, as described above, is the Electrostatic Precipitator and, like the disposable filters, is only intended to remove visible smoke particles from the exhaust airstream rather than the gaseous

through the neutralising section the air is

phase that tends, to account for most of the cooking odours. Therefore, this should not

cooled to remove excess heat, 20% is discharged at low level as clean air to

be considered as a prime source of odour

control. Where installed, panel filters

atmosphere and the remaining 80% can be reintroduced into the kitchen as make-up

should be fitted both upstream and


downstream of the electrostatic filter to • Special ultra violet lights can be installed, either within the filter housing, ventilated ceiling plenum or as a remote unit, which generate trace quantities of ozone. In the presence of ultra violet light, the ozone reacts with the organic compounds in the fat, odour by photolysis and ozonolysis to

provide some protection from larger contaminant that may have passed through

the grease filters. It should be noted that electrostatic filters become ineffective at temperatures over 60°C and are not suitable for relative humidity levels above 75%.

• Activated carbon provides an effective medium for eliminating odour but can be easily rendered disfunctional through the impregnation of contaminants within its porous granule composition. Grease is the

worst such contaminant; it is therefore essential to protect the carbon cells with multi-stage pre-filters upstream of the system. The maximum operating efficiency

of carbon filters is very much dependant

upon them working within defined conditions - an air temperature not exceeding 40 deg C and a maximum relative humidity of 60%. To maximise best

use of carbon cells a strict maintenance regime for changing all filters shall be adopted. Local Authority approval shall be


leave an end product of primarily only carbon dioxide and water.



type of pollution control is

implemented, the increase in system resistance shall be included when selecting the fan.

DW/1 72 Sveiz for Kitchen Ventilation Systems


mesh absorbs heat from the exhaust and alternately transfers it to the supply air. (Approx 80% efficient)

Heat Recovery 23.1 Whilst the initial capital cost may be high, the use of heat recovery for its energy efficiency

and conservation value is becoming an increasingly important design feature. If a specific payback period has to be achieved. then calculations should be made to evaluate an economic timescale.


There are two main methods of recovering heat

in a kitchen environment:

Air to Air -


removal of heat from the

exhaust air which is transferred to the incoming supply air.

• Heat Pipes - These are self contained units operating on a vaporising / condensing cycle. Hot exhaust air causes fluid in the lower part of the pipes to evaporate and transfer heat to the supply air passing over the upper section. The vapour cools and

condenses for the cycle to start again (approx 55 to 70% efficient).

It should be noted that, with the exception of

the run around coils, these arrangements require the supply and extract ductwork to be run in close proximity.

23.4 It is important that whichever heat recovery option is incorporated. it shall be protected

Air to Water - The removal of heat from the exhaust air which is transferred to a domestic

from grease build-up by the installation of air filters upstream of the equipment.

water supply.



selection of waste heat recovery plant

should be from the following types:

• Heat Recuperator - Plate heat exchangers of the 'cross flow' type having adjacent plates forming narrow ducts for alternate supply and exhaust air to pass. Heat is transferred

through the plates with no crosscontamination between the air passages (60 - 80% efficient). A face and by-pass damper shall always be included to allow fresh air to

by-pass the recuperator when further heating to the room being served is no longer required.

• Run Around Coils - Coils can be fitted across the extract and supply ducts whereby

the higher temperature of the extract air transfer heat to a water/ethylene glycol mix in the interconnecting pipework (50 - 60%

efficient). A circulating pump and pressurisation provisions are required for the pipework system.

• Rotary Recuperator Consists


Wheel) -

of a revolving cylinder divided

into segments packed with coarsely-knitted

metal mesh. As the cylinder rotates, the

— 49

DW/1 72 Specification for Kitchen Ventilation Systems


24.4 The air velocity passing through the filter or grille shall be first determined by using an anemometer. This figure is then multiplied by the face area of the filter or grille to arrive at

Testing and Commissioning

the extract flow rate. The flow rate through

each filter is then added to give the total quantity of air being extracted through each

24.1 This section covers the requirements for testing the completed installation. The

canopy. This is then checked to ensure that the design conditions are being achieved.

responsibility for this will depend upon the particular contract provisions.



determine the air volume flow rates through

The following information shall be recorded

the ductwork, but care shall be taken to ensure that readings are taken in areas where there is

during the testing and commissioning process.

The supply and extract systems shall be

little turbulence such as in straight runs of ductwork so that the results do not become

operating simultaneously when commissioning is carried out.

• The velocity through the grease filters and




point of discharge of the extract should not increase the overall ambient noise level by


more than 2db(A) on completion of the

• The supply and extract flow rates.

installation. The use of vertical discharge, slow

running fans and low duct velocities should

• Ambient and air temperatures in the

help to achieve these levels.


• Starting and running currents used by the fan(s).

• Illumination levels. • Sound levels in the kitchen and at the point of discharge.

24.3 The manufacturer's data shall be consulted to establish the technical information on the filters and the three most important items are:

• Flow rate for each filter size used.



installed canopy or ventilated ceiling

shall be fitted with a 'rating plate'. For canopies this shall be on the inside left end of

each canopy on which the following information shall be recorded.

• Name, address and telephone number of the canopy supplier.

• Date of installation and canopy serial number.

• Design extract and supply flow rates.

• Design pressure drop across the canopy when measured at the extract spigot.

• Recommended velocity passing through the filter.

• Similar information for any supply system

• The pressure drop across the filter.

This information will be invaluable at a future

• Whilst the grease extraction rate may be

date when upgrades to either the cooking equipment, canopy or ventilated ceiling are

stated, this is not relevant to testing.


Noise levels shall be checked to ensure that a

maximum internal noise level of NR4O-50 is not exceeded and the maximum level at the

• The velocity in the ductwork and at the bell

• The total pressure drop for the system.

Manometers and pitot tubes should be used to

fitted to the canopy.

being considered.

DW/1 72 SpecifIcation for

24.8 Further obtained

Kitchen Ventilation Systems

advice on commissioning may be SECTION from the CIBSE and BSRIA

application manuals (see Appendix F).


Cleaning and Maintenance

25.1 For the efficient operation of a kitchen ventilation system the following maintenance procedures shall be implemented. For detailed requirements refer to the HVCA publication TRII9 Guide to Good Practice - Cleanliness of Ventilation Systems.


interval between visual inspections of elements of the system incorporated in the The

kitchen should be determined by the particular cooking process, but shall never be more than

once a week. All metal surfaces shall be checked to ensure that there is no accumulation

of grease or dirt and that there is no surface damage.



shall be made to ensure that the

stiffening channel is free from debris and that

installed lights are working. Filters shall be easily removable and the inside of all housings

and grease collection drawers, where fitted, should be cleaned regularly.


Typically the minimum cleaning period for

baffle type self draining filters and collection drawers is once each week, for secondary mesh filters at least twice each week. By the nature

of their construction, secondary mesh type filters have a limited life and shall be replaced when necessary. However, specific

manufacturers' information

should be

complied with.

25.5 It should be considered that the area immediately above any cooking appliances, including extract plenums, pose the greatest risk of the ignition of any accumulated grease.

Extract plenums for both canopies and ventilated ceilings are considered as a specific

section of the grease extract system; in the course of a scheduled specialist duct clean, extract plenums should be included by them as

part of the clean. Frequency of cleaning is defined in TRI19 Guide to Good Practice — Cleanliness of Ventilation Systems.


DW/1 72 Specification for Kitchen Ventilation Systems

25.6 All

metal surfaces shall be cleaned with a suitable metal cleaner. Caustic or abrasive

standard. Due to the fact that standard techniques and chemicals used for daily

materials shall not be used as they will scratch the surface which will encourage the growth of

cleaning do not remove the accumulations of carbon fat grease deposits and limescale in

harmful bacteria. Compliance with the

many normally inaccessible areas, all

appropriate COSHH Regulations must be ensured with all cleaning materials.

accessible main ductwork runs and branches, including fitted equipment shall be inspected

and cleaned. To assist in the inspection of 25.7 Where the canopy/ventilated ceiling contains

removable filters or cartridges the filter

ductwork, cleaning doors shall be installed at regular intervals (see section 15.13).

manufacturers cleaning instructions shall be

followed. They shall only be removed for 25.12 Manufacturers shall be consulted for cleaning after the system has been shut-down to avoid grease contaminated air depositing on

maintenance procedures for proprietary plant and fire suppression systems where fitted.

the internal surfaces of the ductwork and therefore causing a future potential fire hazard. Extreme caution shall be exercised if removing

filters from above hot appliances. In general most filters are designed to fit inside, and be

put through the cleaning cycle of most commercial dishwashers. In heavy duty applications decarbonising and/or soak tanks

may prove to be a more effective cleaning method, whilst in lighter applications hand washing in hot water using a standard dilution of a proprietary dc-greasing agent or washingup liquid may be adequate.

25.8 When excessive residue remains following routine cleaning, then a heavy duty detergent or proprietary stainless steel cleaner may be required.

25.9 Where a cartridge system has been installed, then the plenum forms an integral part of the design, it shall be cleaned at the same time as the cartridge. The efficiency of these systems will depend upon the extracted grease that is

collected in the plenum being removed by regular cleaning at least twice a week.

25.10 Where canopies/ventilated ceilings are provided with an integral make-up air system, the airways and supply filters should be kept clean to maintain airflow. Dirt accumulation

and blockages will increase resistance and affect the system performance.

25.1 1 In addition to daily cleaning and a weekly maintenance programme, periodic 'deep hygiene cleaning' shall be undertaken by a specialist contractor to ensure that the food environment maintains a safe and clean


25.13 Where grilles are fitted, they shall have easily removable cores to facilitate cleaning.

25.14 Failure to implement these maintenance procedures, will cause an accumulation of grease and dirt in the ventilation system which will promote the growth of harmful bacteria, increase the risk of fire, reduce airflow through

the kitchen and impair the overall system performance and efficiency (see section 15.12).

DW/l 72 Specification for

Appendix A

• Filters with an initial dust spot efficiency below 20% are classified as 'arrestance filters' (formerly 'coarse G filters') and

Filter Classifications Al

have a 'G' rating of from Gi - G4 with a test pressure of 250 pascals.

18 is included to show the filter classifications based on the European Table

Normalisation standard (EN 779) and their relation to the old EU rating (Eurovent 4/5).


Kitchen Ventilation Systems

The EN standard is more stringent than the old

• Filters with an initial dust spot efficiency

above 20% and an average dust spot efficiency above 40%, are classified as 'efficiency filters' (formerly 'fine F filters') and have an 'F' rating of F5 - F9.

Eurovent classification, and was adopted throughout Europe from January 1994. The new British Standard reference becomes BS EN 779 and the main changes are:

Table 18- Filter Types and Classifications Type

EN 779

New Class

Coarse Dust Filter


Fine Dust Filter

High Efficiency Particulate Air Filter


Test Standard

Gi G2 G3 G4

65% 65% - 80%

Gravametric Arrestance

EN5 (EU) EN6 (EU) EN7 (EU) EN8 (EU) EN9 (EU)


40% 60% 80% 90%

EN1O (EU) EN11 (EU) EN12 (EU) EN13 (EU)


EN 2 (EU) EN 3 (EU) EN 4 (EU)

F6 F7 F8 F9

Hi! H12 H13

80%-90% 90% - 60% - 80% - 90% - 95%

Dust Spot Efficiency


85% 95% 99.5%

D.O.P. Efficiency



DW/1 72 Specitwation for Kitchen Ventilation Systems

APPENDIX B Conversion Factors LENGTH FROM Feet Metres Inches Millimetres


cfm litres/sec cfmlft


Metres Feet Millimetres Inches


MULTIPLY BY 0.3048 3.28 1

25.4 0.0394


0.0004719 2119 0.4719 2.119


cfm litres/sec cfm m3/s per m

m3/s per m

cfm / ft



mIs fpm

PRESSURE FROM Inches wg Pascals

Pascals Inches wg


0.00 1548

646 0.00508 196.85


249 0.00402

WEIGHT FROM Pounds Kilograms

Kilograms Pounds

MULTIPLY BY 0.4536 2.2046




POWER FROM Horsepower Kilowatts

Kilowatts Horsepower

CAPACITY FROM Gallons Litres US Gallons Litres

Litres Gallons Litres US Gallons








0.746 1.34


4.546 0.22 3.785 0.264

MULTIPLY BY 0.2931 3.412

TEMPERATURE To Convert Deg C to Deg F: x 1.8 + 32 To Convert Deg F to Deg C: -32 x 0.556


DW/1 72 Specification for

Kitchen Ventilation Systems

Appendix C Indices of Protection An index of protection known as an IPrating, is an indication of the degree of protection that is provided by the enclosure to a piece of electrical equipment. There are two numbers in an IP rating, the first of which indicates the protection against the ingress of solids and the second its protection against the ingress of liquids.

First Figure

Second Figure Protection



No protection

No protection


Protection against solid bodies larger than 50mm


Protection against vertically falling drops of water


Protection against solid


Protection against drops of rain water at 1 Sdeg from the vertical.


bodies larger than 12mm.


Protection against solid bodies larger than 2.5mm.


Protection against drops of rain water at 6Odeg from the vertical.


Protection against solid bodies larger than 1mm.


Protection against projections of water from all directions.


Protection against dust (no harmful deposits).


Protection against jets of water from all directions.


Complete protection against dust.


Protection against jets of water similar to heavy seas.


Protection against the effects of immersion.


Protection against prolonged effects of immersion under pressure.

These indices are provided in accordance with 1EC529, BS5490 and D1N400 50.


DW/1 72 Specification for Kitchen Ventilation Systems

Appendix D

service may last for days, automatically

operated fire suppression systems are recommended for cooking equipment

Fire Rated and Smoke

involving the use of oils and fats where the

Extract Ductwork

capacity exceeds 10 litres, whether as a single



appliance or a combination of adjacent

When new kitchens are planned, it is important

that the Local Authority Building Control Officer is consulted to ensure compliance with


the Building Regulations and the Fire

atmosphere directly above the equipment it serves. Where this is not possible, the design

Precautions Act. The interpretation of these

statutes may vary according to the Local

shall comply with the requirements of BS 5588

Authority and early consultation will clarify any special requirements with regard to fire rated and smoke extract ductwork. A written record of all advice given should be recorded

compartmentation is breached. This currently requires that in all non-domestic where


and retained.


• Ductwork carrying polluted air must have separate and independent extraction with no recirculation.

main fire hazard arises from the overheating of oils and fats in frying The

equipment and the failure of temperature

• No fire dampers are to be installed in the

monitoring devices. Safe cooking in fats and oils generally takes place below 200 degC. Flammable vapours are given off at 200 - 230 degC and spontaneous ignition occurs at 310 -

extract ductwork.

• If immediate discharge to atmosphere is not

possible and the ductwork needs to pass

360 degC. The timescale in moving from a safe

through an adjacent fire compartment, then the ductwork system must be satisfactorily

to dangerous condition is quite short and the

flash point of oil is reduced by repeated

constructed and supported in order to

oxidation caused through repeated use. Further

maintain the required level of fire

advice is available from the Fire Protection

separation between compartments.

Association's guides to safe practice.


• It is essential that the installed system


procedures while cooking, poor planning of the kitchen layout, failure to

complies with BS 476. Fire inside (Type B) is rated for stability, integrity and insulation

maintain equipment and poor waste disposal procedures all lead to an increased risk of fire.



for the same period of time as the compartment through which the duct passes. In addition the duct shall also be tested for fire outside (Type A) with the additional requirement that the internal

mechanical ventilation to a kitchen,

although essential, can exacerbate the consequences of a fire and it must be purpose designed to contain damage or injury that may

surface of the ductwork within the compartment shall also meet the insulation criteria.

occur from smoke and toxicity. The system must be separate from and independent of all other systems in the building.



• Where canopies are installed on separate floors, then they shall be served by separate extraction systems

involving a deep fat fryer and its extraction system will develop rapidly, Fire

produce considerable quantities of heat and smoke, it may reach a stage of such violence that it cannot be contained within the kitchen area. Due to the fact that equipment damage may be significant and disruption to normal

The extract from equipment using oils or fats should be as short as possible and discharge to


There are three ways of protecting ductwork recommended in BS 5588 where compartmentation is breached. These are

defined in DW/144 Appendix D and summarised as follows:

DW/1 72 SpecifIcation for

Method I covers the provision of fire dampers located where the duct penetrates fire resisting

system unless the materials and construction of

compartments such as walls or floors. The

requirements of BS 3476.

the whole system is in accordance with the

ductwork itself is not fire resistant but the fire is not transferred through the system. Due to D1O the fact that fire dampers are not permitted in kitchen extract systems, this method shall not be used.

Method 2 is where the duct runs within a fire rated service duct from the kitchen directly to the outside of the building. The service duct

forms a compartment known as a protected shaft which must not contain any other services or have fire dampers fitted. This method may be used.


fire outside the duct does not cause any grease

that has built up on the inside of the duct to ignite. The insulation shall ensure that temperatures on the outside of the duct shall

The requirements for smoke extract ductwork will vary from Authority to Authority and will generally depend upon the size of the building, the area of openable windows, the number of occupants and whether the area to be ventilated

is located in the basem*nt. With the use of motorised volume control dampers, it may be

possible to use either the supply or extract ductwork as smoke extract ductwork provided that it is constructed to the same standards as fire rated ductwork with additional care taken

applied to suitably constructed and supported conventional ductwork. Care shall be taken

when providing extract ductwork which is

fabricated from fire rated boards, as the boarding itself may absorb grease and be

over the selection of the plant. Where the supply ductwork is used as smoke extract, then any filters installed will need to be by-passed.

incapable of being cleaned.

In all cases where fire rated ductwork is supplied, particular care shall be taken with the design of both fixings and supports to ensure that they are suitable for the specified duration of fire protection . If a fire originates in or is transferred to the ductwork system, then it may spread beyond its original location due to heat

fire rating of kitchen extract ductwork shall also include insulation, to ensure that a


not exceed 140 degC average above ambient at any one point.

Method 3 is where the duct is in itself fire resistant and this is achieved by either the ductwork being constructed from fire rated materials, or where a protective material is


Kitchen Ventilation Systems

Smoke extract ductwork must also be constructed so that in the event of a fire, it will retain at least 75% of its design cross sectional area.

Dl 2

A natural make-up air system shall be installed to provide the equivalent amount of air as the

design volume for the smoke extract system

radiation or direct contact between the

and the discharge shall be located to avoid any

ductwork material and an adjacent combustible

risk of recirculation of smoke back into the

material. The ductwork route shall therefore


take account of this risk, have a minimum separation of 500mm between uninsulated Dl 3 Smoke extract fans need to be located within I ductwork and any combustible material.



both fire rated and smoke extract

ductwork, the periods of stability, integrity and

insulation to which the ductwork is constructed, must be the same as the rating of the compartment that is being breached. The

construction of fire rated ductwork, which D14

hour fire rated compartments and motors must be rated to a minimum of 300degC for 1 hour (varies with Local Authority). Wiring shall be installed within protected circuits with power supplied by a back-up generator in the event of failure of the main source of power. Further information on fire rated and smoke

shall comply with BS 476, can either be

extract ductwork can be found in the

provided by specialist companies producing proprietary systems, or by the addition of fire

Association of Specialist Fire Protection's publication "Fire Rated and Smoke Outlet

insulating materials to suitably constructed and supported ductwork. General purpose ductwork cannot be converted into a fire rated

Ductwork - An Industry Guide to Design and Installation" (aka the Blue Book).


DWII 72 Specification for Kitchen Ventilation Systems

Appendix E Air Conditioned Kitchens El

Section 5 showed that the two main sources of

heat into a kitchen space comprised: Radiant - 35% (Qrad) Convective - 65% and (Qconv)



estimating the air conditioning load

however, it is also necessary to consider other

heat gains such as those caused by lighting, solar, and people - (Qgen).


The amount of Qrad and Qconv will vary with

the type of cooking equipment and the extract flow rate through the hood shall be equal to or

Fig 23 - Pattern of Heat Gain in Kitchen


heat load (Qtot) can be calculated by using the following energy balance equation:

higher than the convection flow from the appliances to ensure that the Qconv and the

Qtot = Sensible Heat (Qsens)+Latent Heat (Qlat)

associated impurities are captured by the canopy (see fig 22).


It should be noted that the latent heat element is normally insignificant in relation to the total heat gain in a kitchen environment and if air conditioning is provided, then it is usually in the form of comfort cooling as opposed to total control of both temperature and humidity, as the capacity and cost of the plant required may not be in proportion to the benefit derived.

Depending on the efficiency of the extraction

system, there may also be an amount of convective heat that is not captured by the canopy (Qesc), together with the radiant heat

(Qrad) and general gains (Qgen), can be treated by means of an air conditioning system (see fig 23).


An inefficient canopy with a low capture

efficiency (Heff) will therefore have a significant effect on the air conditioning load, and the relationship between canopy efficiency and the amount of convective heat not being captured can therefore be expressed as:

Once these variables are established, the total


However, when the total load is required for air

conditioning assessment, then each element can be calculated using the energy balance equation shown in Fig. 24.

Qesc = (1-Hem x Qconv.

QRAD 35%

Fig 22 - Proportion ofAppliance Heat Emission


QRAD 35%

DWII 72 Specification for Kitchen Ventilation Systems



the amount of supply air required

exceeds that which may be supplied through the canopy, then additional grilles and diffusers should be provided as part of the main HVAC

system and positioned to provide optimum comfort cooling for the staff.


To summarise, both the extract flow rate and

the supply air volume shall be calculated to ensure that both the convective and radiant

heat generated is removed to maintain an acceptable level of comfort for the occupants of the kitchen. (NB - air conditioning of the kitchen will not remove the direct discomfort caused by radiant heat emanating from the cooking equipment)

Sensible Heat Qsens=P x cpm x At x qs (kW) Latent Heat Qlat = P x Hfg x Ag x qs (kW) (specific latent heat of evaporating heating from tables for properties of water and steam)


Qsens = Qrad + Qesc + Qgen. (kW) (where Qesc = (1-Heft) x Qconv)

Qiat = latent heat given off by occupants etc. (kW) = density of air. (kg/m3) P Cp = specific heat capacity of air. (kj/kg degC) temperature difference between supply



Ts) and room condition (Tr) (deg C) (normally 8 - 10 degC) (Printers note A = Delta) Ag = moisture content difference between supply air (Gs) and room condition (Gr) (kg/kg) (Printers note - A = Delta) = qs supply air flow rate (m3/s) Hfg = latent heat energy of moisture at room conditions (kjlkg) (latent heat of vaporisation from steam tables) Fig 24 - Heat gain calculation


DW/1 72 Spccijication for Kitchen Ventilation Systems

Appendix F

Chartered Institution of Building Engineers (CIBSE) Tel: 0208 675 5211


CIBSE Guide B: Installation and equipment data



Association for Specialist Fire Protection (ASFP) ISBN 0 900953 30 6. Section B2.B3: Ventilation and air conditioning (requirements and systems, equipment Tel: 01252 739142 Fire Rated and Smoke Outlet Ductwork: An Industry and control). Guide to Design and Installation (Blue Book) CIBSE Code for Lighting (2002) Building Services Research and Information ISBN 07506563 79

Association (BSRIA) Tel: 01344 426511 Application Guide LB65/94: Ventilation of Kitchens

Commissioning of Fire Systems in Buildings (1994) ISBN 086022 2314

Fire Risk Assessment - Catering Extract Ventilation

CIBSE Commissioning Code A (1996) Air Distribution Systems ISBN 0900953 73 X

Technical Memorandum 13 (2002) Minimising the risk of Legionnaires Disease ISBN 1 903287 23 5

ISBN 056022 588 7

CIBSE Guide B2 (2001): Ventilation and air

9000 BS 476:

Fire Tests on Building Materials

HMSO Tel: 020 7276 5203

Part 24: 1987

Fire Resistance of Ventilations Ducts


conditioning ISBN 1903287 16 2 (requirements and British Standards Institution (BSI) Tel: 0208 996 systems equipment and control)

Fire Precautions (Workplace) Regulations 1997 No

BS 4142: 1997 Rating of Industrial Noise Affecting Food Safety (General Food Hygiene) Regulations 1995

Mixed Residential and Industrial ISBN 0110 532279 Areas

BS 5440: Part 1 Specification for Installation of flues

The Gas (Installation and Use) Regulations 1998 (S.I. 1998 No 2451)

BS 5440: Part 2 Specification for installation of gas HSC HSE Books Tel: 01787 881165 appliances

BS 5588: Part 9 1999

Fire Precautions in the Design and ISBN 0717617726 Construction of Buildings

B5 5720: 1979 Code of Practice for Mechanical Ventilating and Air Conditioning in Buildings BS 6173

Legionnaires Disease - Approved Code of Practice and guidance L8

Workplace (Health, Safety and Welfare) Regulations 1992. Approved Code of Practice and Guidance L24. ISBN 0717604136

HSE Information Sheet: Ventilation of kitchens in

Installation of gas-fired catering catering establishments. Catering Sheet No 10 appliances for use in all types of catering establishments (2nd and 3rd family gases)

NOTE: The European/British Standards and other documents listed above are those available at the date of publication. Users should ensure that they consult the latest version.


DW/1 72 SpecifIcc!tioi! for

Kitchen Ventilation Systems

Heating and Ventilating Contractors' Association Tel: 020 7313 4900 1998 - Specification for Sheet Metal DW/144 Ductwork iSBN 0-903788-27-4

TR/19/1 -

2005 - Guide to Good Practice Cleanliness of Ventilation Systems

ISBN 0-903783-26-6 DQ/143 -

2000 -

JS2 1/CD-Rom -

COSHH Manual 1 Advice on

Practical Guide LeakageTraining ISBN 0-903783-30-4

to AV

compliance with the Regulations

Joint Hospitality Industry Congress (JHIC) Tel: 01582 424200 Catering Industry Guide to Food Safety (General Food Hygiene) Regulations 1995 ISBN 0-900-103-00-0 Loss Prevention Council (LPC) Tel: 0208 207 2345

1996 16A16B -

Fish and chip Frying Ranges Cooking Equipment (other than fish and chip frying ranges)

LPS 1263 -



Office of the Deputy Prime Minister The Building Regulator 2000 Approved Document B ISBN 0-1 1-75391 1-2


DW/1 72 Speckation for Kitchen Ventilation Systems



DW/1 72 SpecifIcation for

Kitchen Ventilation Systems



DW/1 72 Speckation for Kitchen Ventilation Systems



For a full list of available titles, please contact (lie HVCA

Publications Unit on

01768 860405 or

our website at


HVCA HVCA Publications Old Mansion House Eamont Bridge Pen ri di


Cu bri a CAIO 2BX

Heating and Ventilating Contractors' Association Esca

House 34 Palace Court

London W2 4113 Tel: 020 7313 4900 Fax: 020 7727 9268

e-mail: [emailprotected] website: www hvca.org.uk

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