If you are fitting out a commercial kitchen in the UK, DW172 is the document your extraction system will be measured against. This page explains what it covers, what it does not, and how it fits with the other rules that apply to a catering kitchen. It is written for operators and project managers rather than for ventilation engineers.
What is DW172?
DW/172 is the Specification for Kitchen Ventilation Systems, published by the Building Engineering Services Association (BESA). It is the recognised UK standard for how commercial kitchen ventilation is designed, built, installed and maintained, covering canopies, grease filtration, ductwork, fans and discharge.
DW172 is a specification, not legislation. Nobody will prosecute you for failing to follow DW172 by name. What happens instead is that it becomes the benchmark: main contractors write it into the specification, insurers expect it, environmental health officers use it as the reference point for what “reasonable” looks like, and it is the document an expert would be asked about if something went wrong. In practice, building to DW172 is how you demonstrate you have done the job properly.
What DW172 covers
- Canopy design and sizing. How far the canopy must extend beyond the cooking line, the height it sits at, and the extract volume needed for the appliances underneath it. [CONFIRM: minimum overhang and mounting height figures.]
- Grease filtration. Filter type, filter face velocity and the provision of a grease collection route. Baffle filters are the expected standard on a cooking canopy.
- Ductwork construction. Material, gauge, jointing and the requirement that grease laden ductwork is built so it can actually be cleaned. [CONFIRM: duct velocity range for grease laden extract.]
- Access for cleaning. Access panel size and spacing along the duct run, including at every change of direction.
- Make up air. Replacement air to balance what is being extracted, so the kitchen does not go into negative pressure and drag air from the dining room.
- Discharge. Where the discharge terminates relative to openings, neighbours and the building line, and when odour control is needed.
- Commissioning and handover. The measured results and the record that the system does what it was designed to do.
What DW172 does not cover
DW172 sits inside a wider set of rules. The ones that usually matter on a catering project are:
- BS 6173, the standard for installing gas fired catering appliances. This is where the requirement for a gas interlock comes from: gas appliances must not be able to run unless the ventilation is running and proving.
- The Gas Safety (Installation and Use) Regulations 1998, which is the legal backing behind the above.
- Building Regulations, in particular Part F on ventilation, Part B on fire safety and Part J on combustion appliances.
- The Workplace (Health, Safety and Welfare) Regulations 1992, which require workplaces to have effective and suitable ventilation.
- Food hygiene regulations, which require the kitchen to be ventilated well enough to prevent condensation, mould and the contamination that follows.
- BESA TR/19 Grease, which covers cleaning the system once it is in use. DW172 gets the grease out of the air. TR/19 keeps the duct clean afterwards. Your insurer is more likely to ask about TR/19 than about anything else on this page.
Gas interlocks and DW172
This is the single most common compliance gap we see on existing kitchens. If there are gas appliances under the canopy, an interlock is required. It ties the gas supply to the ventilation so that the gas solenoid valve cannot open unless the extract fan, and where fitted the supply fan, are proven to be running.
There are two common approaches. An air pressure proving system senses actual airflow in the duct. A current sensing system monitors the fan motor’s current draw. Air proving is the more thorough of the two because it detects a blocked filter or a slipped belt, not just a fan that is powered up.
CK Direct supplies Merlin gas interlock kits for both approaches.
What this means when you specify a system
A DW172 compliant system is not a product you buy, it is a set of decisions made in the right order:
- Start with the appliance schedule. The cooking line determines the canopy size and the extract volume. Everything downstream follows from it, so a schedule that changes after the canopy is made is an expensive change.
- Size the canopy to the line, not to the room. The canopy has to overhang the appliances, which usually makes it larger than people expect.
- Work out where the duct can physically run and where it can discharge, before committing to a layout. Discharge position is the thing most likely to cause a planning problem.
- Size the make up air at the same time rather than as an afterthought.
- Design in the cleaning access from the start. Retrofitting access panels into a live kitchen is disruptive and costly.
- Interlock the gas if there are gas appliances.
- Commission it and keep the paperwork. The commissioning record is what you produce when someone asks.
CK Direct designs, manufactures and installs to this specification from our Peterborough workshop. See commercial kitchen extraction systems, or read how we work through design, manufacture, install and maintain.
Frequently asked questions
Is DW172 a legal requirement?
No. DW172 is an industry specification, not legislation. The legal requirements come from the Building Regulations, the Gas Safety (Installation and Use) Regulations and workplace health and safety law. DW172 is how the industry demonstrates those requirements have been met, which is why it ends up written into specifications and asked about by insurers.
Do I need a gas interlock in a commercial kitchen?
If the kitchen has gas fired catering appliances under a canopy, yes. BS 6173 requires that gas appliances cannot operate unless the ventilation is running and proven. It applies to existing kitchens as well as new ones.
Does commercial kitchen extract ductwork have to be fire rated?
It depends on the route the duct takes and the compartments it passes through, which is a Building Regulations Part B question rather than a DW172 one. [CONFIRM: how far CK Direct wants to go on fire rating advice, given it is usually the fire engineer’s call.]
How often should a kitchen extraction system be cleaned?
Cleaning frequency follows the cooking hours and the type of cooking, and is set out in BESA TR/19 Grease rather than DW172. [CONFIRM: whether to quote the TR/19 frequency bands here.] Filters need washing far more often than the ductwork needs cleaning.
What extract rate does my kitchen need?
It is calculated from the appliances under the canopy, their type and their duty, not from the size of the room. Two kitchens of identical floor area with different cooking lines will need different extract volumes. Send us your appliance schedule and we will calculate it.
Does DW172 apply to a recirculation unit?
Ductless recirculation units solve a different problem, which is a site where ductwork to outside is not possible. [CONFIRM: what CK Direct wants to say about where DW172 does and does not bear on ReCirc units, and about the appliance types they are suitable for.]
Downloads
Our design guide covers the same ground with the drawings and the numbers: