Compliance · 2026
DW172 Ventilation Explained
DW172 is the specification that governs how commercial kitchen extraction is designed, installed and signed off. Get it wrong and an EHO can stop you trading, your insurer can walk away from a grease-fire claim, and the system comes out and goes back in at your cost. Here is what DW172 ventilation actually requires, and what it means for your kitchen.
The short answer
What DW172 actually is
DW/172 is the Specification for Kitchen Ventilation Systems, published by BESA (the Building Engineering Services Association). The current version is the 2nd edition, which incorporates the April 2020 addendum. It is the recognised UK benchmark for the design, installation, testing, commissioning and maintenance of commercial kitchen extraction and ventilation.
DW172 is not an Act of Parliament, so on its own it is not "the law". But that distinction matters less than operators think. Environmental Health Officers, building control, fire risk assessors and insurers all treat DW/172 as the standard a compliant system is measured against. If your extraction does not meet it, you are exposed on every one of those fronts.
It is also a whole-system specification, not a canopy rule. DW172 covers the parts most operators never see:
Canopy and capture design
How the canopy is sized and positioned over the cooking line so heat, grease and fumes are captured before they reach the kitchen.
Ductwork construction and routing
Material, joints, transport velocity and the route the duct takes from canopy to fan to discharge.
Extract and make-up air balance
Replacement air sized to match what is extracted, so the kitchen does not run in negative pressure.
Fire-rated ductwork and suppression interface
Fire-rated construction where ducts pass through compartments, and how the system ties into fire suppression.
Access for cleaning
Access panels along the full duct run so the system can be cleaned to TR/19 throughout its life.
The stakes
Why DW172 ventilation matters
Four things hang on getting this right. Any one of them is enough to shut a kitchen.
EHO sign-off
An Environmental Health Officer can refuse to approve a kitchen for trading if the extraction does not meet recognised standards. On a new fit-out that means no opening date. On an inspection it can mean an improvement notice with a deadline you cannot hit without ripping the system out.
Insurance
Most commercial policies require ventilation installed to DW/172 and cleaned to TR/19. A grease fire in a system that was never compliant, or has no access panels to clean, is the fastest way to have a claim refused after the worst has already happened.
Planning and building control
Discharge position, odour control and noise are routinely conditioned on planning consent, and building control will expect ductwork that meets fire-compartmentation requirements. A non-compliant route can stall a project after the equipment is already on site.
Staff safety and performance
An undersized or unbalanced system pulls the kitchen into negative pressure. Doors slam, gas appliances are starved of air, fumes hang in the room and the extraction never does its job. DW172 exists to stop exactly that.
In practice
What it means for your design
This is where DW172 stops being a document and starts costing or saving money. The detail that follows is what a designer should be working to from the first drawing.
Canopy overhang
The canopy should extend at least 300mm beyond the front and sides of the cooking equipment. Overhang is what captures the rising plume of heat and grease before it escapes into the room. Skimp on it and the canopy is fighting the cooking line from the start.
Duct sizing and velocity
Ductwork is sized to hold a transport velocity that keeps grease-laden air moving rather than settling on the duct walls. Too slow and grease drops out and builds up; too fast and you pay for it in fan energy and noise. It is a balance, set by the extract volume, not a guess.
Access panels
Access doors at regular intervals along the whole duct run, so every section can be reached and cleaned to TR/19. A duct you cannot access is a duct you cannot clean, and an uncleanable duct is a fire risk and a failed inspection waiting to happen.
Make-up air
A make-up air (MUA) supply sized to replace what the system extracts. Without it the kitchen runs in negative pressure, which kills extraction performance and can pull combustion products back out of gas appliances. On most commercial kitchens MUA is not optional.
Fire-rated ductwork and suppression
Where ducts pass through fire compartments they need fire-rated construction, and the extraction has to interface cleanly with wet-chemical fire suppression so a canopy fire shuts the system down and is dealt with, not fed.
Grease management
Baffle filters and grease capture at the canopy do the first stage of the job, keeping as much grease as possible out of the duct in the first place. The less grease that gets past the filters, the longer and safer the system runs between cleans.
All of this is in scope on every extraction system we design. See our commercial kitchen extraction page for how we handle canopies, ductwork, MUA and gas interlock in-house.
Setting it straight
Common misconceptions
"DW172 is just about the canopy"
The canopy is the visible part. DW/172 governs the whole system, ductwork, fans, make-up air, fire rating and cleaning access included. A perfect canopy on a badly routed, inaccessible duct is not a compliant system.
"A recirculation unit means I can skip it"
DW/172 covers recirculation and demand-controlled systems too. Going ductless changes the design problem, it does not remove the standard. The filtration, balance and maintenance still have to be right.
"Any builder can run the ductwork"
Grease-extract ductwork is a specialist job. Wrong material, leaking joints, no fall, no access panels and a route through a compartment with no fire rating are the faults we are called in to put right, usually after a failed sign-off.
"It's a one-off at installation"
DW/172 runs through the life of the system. Cleaning to TR/19, filter changes and access for inspection are part of staying compliant, not a one-time box ticked on handover day.
The downside
What happens if extraction isn't compliant
The cost of a non-compliant system is rarely the system itself. It is the trading days lost, the claim refused, and the second installation you pay for because the first one failed.
On a new project, a system that does not satisfy the EHO or building control means no sign-off and no opening. On an existing kitchen, an improvement notice puts a clock on works you may have to do mid-service. And if a grease fire takes hold in a system that was never built or cleaned to standard, the insurer has every reason to decline the claim, leaving the fire damage, the lost trade and the rebuild all on you.
The fix is to get the extraction right at design stage, before equipment is ordered and ductwork is in the ceiling. You can read the full specification on the BESA website, or have us check your scheme against it. The cheapest time to find a DW172 problem is on a drawing, not at sign-off.
If you are scoping a new kitchen or a refurbishment, book a free site survey and we will tell you exactly what your extraction needs to meet the standard.
Common questions
FAQ
Is DW172 a legal requirement?
DW/172 is a specification, not legislation, so it is not "the law" in its own right. In practice it is treated as the benchmark for a compliant commercial kitchen ventilation system by Environmental Health Officers, building control, fire risk assessors and insurers. Underlying legal duties, including health and safety, building regulations and fire safety, are most easily satisfied by building to DW/172, which is why it carries the weight it does.
Who signs off DW172 compliance?
There is no single DW172 certificate. Compliance is demonstrated through the installer's commissioning records, the system design and the ongoing cleaning regime, and it is assessed by the EHO at inspection, by building control where applicable, and by your insurer when a policy is taken out or a claim is made. A competent installer should hand over commissioning documentation that shows the system was designed and tested to the standard.
Does my existing kitchen extraction need to meet DW172?
An older system installed before the current edition will not always match it line for line, and there is no automatic requirement to rip out a working system. But if you are refurbishing, if an EHO has raised concerns, or if your insurer asks questions after an incident, the system will be judged against current standards. The practical answer is to have it assessed: many older systems can be brought up to standard with access panels, balancing and cleaning rather than a full replacement.
What is the difference between DW172 and TR19?
DW/172 covers how the system is designed and installed. TR/19 is the standard for cleaning grease-extract ductwork once it is in use. They work together: DW172 requires the access panels that make TR/19 cleaning possible, and your insurer will typically expect both, a system built to DW/172 and cleaned to TR/19 at the right frequency.
Does a recirculating ventilation system need to comply with DW172?
Yes. DW/172 covers recirculation and demand-controlled kitchen ventilation as well as conventional ducted extract. A ductless or recirculating unit changes the filtration and design approach but does not exempt you from the standard. The filtration stages, air balance and maintenance still have to be specified and maintained correctly.
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