Kitchen extract cleaning and why it's needed
Every commercial kitchen that fries, grills or chargrills produces grease. That grease doesn't stay in the pan. A fine mist of fat and oil is drawn up through the canopy, past the filters, and into the ductwork that carries cooking fumes out of the building. Over time it settles on the inside of that ductwork as a sticky, flammable layer — and the longer it's left, the thicker it gets.
Kitchen extract cleaning is the process of removing that grease build-up from the whole system: the canopy, the filters, the fans and, crucially, the ductwork running from the kitchen to the discharge point outside. This post explains why it matters, what the standard expects, and how to keep on top of it.
Why grease in ductwork is a fire risk
Grease is fuel. A layer of cooking fat coating the inside of an extract duct is exactly the sort of thing a flame will travel along, and kitchen extract systems sit directly above the heat sources that can ignite it.
The danger is compounded by the layout. Ductwork runs through ceiling voids, up risers and between floors — the parts of a building you can't see and can't easily reach. A fire that starts in a dirty duct can spread quickly through those concealed spaces, bypassing the compartmentation that's meant to hold a fire back. By the time anyone notices, it may have travelled well beyond the kitchen.
Kitchen extract fires are a recognised and recurring cause of serious commercial fires, and grease build-up is almost always the common factor. The cleaning isn't a cosmetic exercise — it removes the fuel before it can catch.
What the guidance says: TR19 and TR19 Grease
The recognised benchmark for ductwork cleanliness in the UK is TR19, published by the Building & Engineering Services Association (BESA). The specific guidance for kitchen extract systems is set out in TR19 Grease, which deals with grease-laden ventilation.
TR19 Grease measures cleanliness by the thickness of grease deposit left on internal surfaces, verified by testing rather than visual inspection alone. A system is only considered clean when deposits are reduced to the level the standard sets out. "It looks fine" is not a measurement — TR19 Grease exists precisely because grease accumulates where you can't see it.
It also expects the full system to be cleaned, including the sections of ductwork that are hard to access. Where there aren't enough access panels to reach and clean the whole run, part of a proper clean is installing them. A system where only the visible parts have been wiped down has not been cleaned to standard.
Why it matters for insurance
Most commercial insurance policies for premises with catering operations require kitchen extract systems to be cleaned to a recognised standard — in practice, TR19 Grease — at a stated frequency. This is often a condition of cover, not a suggestion.
If a fire starts in a grease-laden duct and you can't demonstrate that the system was being cleaned and verified properly, an insurer may reduce or refuse a claim. That's why the evidence matters as much as the work: a compliant clean should come with a report showing before-and-after measurements, photographs of the ductwork internals, and a record of which sections were accessed and cleaned.
Keep those reports. They are the proof that the work was done to standard, and they sit alongside your other fire safety records.
How often should it be cleaned?
Frequency depends on how heavily the kitchen is used and what's being cooked. The more frying and chargrilling, and the longer the hours, the faster grease builds up. As a general guide:
- Heavy use (12+ hours a day, lots of frying/grilling): clean roughly every three months.
- Moderate use (6–12 hours a day): clean roughly every six months.
- Light use (under 6 hours a day): clean roughly every twelve months.
Treat these as starting points, not fixed rules. The right answer is driven by the actual condition of the system. If an inspection finds grease building up faster than expected, the interval needs to shorten. A post-clean report should recommend when the next clean is due based on what was found.
The responsible person's duties
Under the Regulatory Reform (Fire Safety) Order 2005, the responsible person must manage the fire risks in the premises, and in a catering environment that includes the extract system. A grease-laden duct is a foreseeable fire risk, and ignoring it is a failure to manage it.
In practice that means:
- Knowing where your ductwork runs and whether the whole system can be accessed for cleaning.
- Having the system cleaned to TR19 Grease at an appropriate frequency.
- Keeping the reports and verification records as evidence.
- Reviewing the cleaning interval if use changes or if inspections show faster build-up.
This also feeds into your fire risk assessment. If the assessment doesn't consider the extract system, it isn't complete.
What a proper clean involves
A clean carried out to standard should:
- Inspect first — assess the system, identify access points and record the starting condition.
- Install access where needed — fit panels so every section of ductwork can be reached, not just the easy parts.
- Clean the whole system — canopy, filters, fans and the full length of ductwork to the discharge point.
- Verify the result — measure grease deposits against the TR19 Grease benchmark to confirm the system is actually clean.
- Report — provide documentation with measurements, photographs and a recommended next service date.
If a quote covers only the canopy and filters and says nothing about the ductwork, it isn't a full extract clean — and it won't satisfy either the standard or your insurer.
The bottom line
Kitchen extract cleaning removes the grease that turns your ventilation system into a fire path. It protects the building, keeps your insurance valid, and is part of the fire safety duties you already hold as a responsible person. Clean the whole system, clean it often enough for how you cook, and keep the evidence that proves you did.
If you're not sure whether your current cleaning meets TR19 Grease — or whether your ductwork can even be fully accessed — an inspection is the place to start.