Guide from the team
TR19 Grease links extract cleaning frequency to daily cooking hours. Here is the schedule, and why waiting until it looks dirty is not a policy.
Published 8 September 2026
It is the most common question we are asked about kitchen extract systems, and it has a clearer answer than most people expect. BESA’s TR19 Grease specification does not leave frequency to guesswork: it links the cleaning interval directly to how many hours your kitchen cooks each day.
TR19 Grease groups kitchens into three bands by daily usage:
| Usage | Daily cooking hours | Cleaning frequency |
|---|---|---|
| Heavy | 12-16 hours per day | Every 3 months |
| Moderate | 6-12 hours per day | Every 6 months |
| Light | 2-6 hours per day | Every 12 months |
The logic is simple. Every hour of cooking loads the extract airstream with vaporised fat and oil, which condenses on the inside of the canopy, ductwork and fan. More hours means faster build-up, and faster build-up means a shorter interval between cleans.
Behind the table sits a measured trigger: TR19 Grease treats a mean grease deposit of 200 microns, measured by wet film thickness test, as the point at which a system needs cleaning. The usage bands are the practical schedule that keeps a typical kitchen below that threshold. We cover the test itself in how grease is measured in kitchen extract.
The table is a starting point, not a promise. Several factors cause grease to accumulate faster than the usage band alone would suggest, and a competent surveyor will take them into account.
Cooking style. A kitchen doing heavy frying, chargrilling or wok cooking sends far more airborne grease into the extract system than one steaming vegetables for the same number of hours. Solid-fuel cooking is the extreme case: charcoal grills and wood-fired ovens add combustion products to the grease load and are widely treated as needing more frequent attention regardless of daily hours.
The shape of the system. Long vertical risers deserve particular caution. Grease that condenses in a vertical duct can run and pool, deposits are harder to inspect, and in a fire a vertical run acts as a chimney, carrying flame upwards through the building fast. Systems with long horizontal runs, multiple changes of direction or limited access also accumulate and hide grease in ways a short, simple run does not.
Filtration and containment. Missing, damaged or poorly maintained grease filters let more grease pass into the ductwork, shortening the real interval however good the schedule looks on paper.
This is why we survey before we quote. The band gives the baseline, the survey confirms whether your system needs something tighter.
Plenty of kitchens still clean the extract system when someone notices it looks bad. That policy fails for three reasons.
First, you cannot see the risk. The visible parts of the system, the canopy and filters, are the parts that get wiped regularly anyway. The danger lives in the ductwork between the canopy and the fan, which nobody looks inside during normal operation. A system can look respectable at the hood and be heavily loaded a few metres in.
Second, it produces no evidence. Your duties under the Regulatory Reform (Fire Safety) Order 2005 are managed through your fire risk assessment, and documented extract cleaning is a condition of cover in most UK commercial policies (policies differ, so check yours). “We clean it when it needs it” satisfies neither a fire risk assessor nor an insurer. A scheduled programme with reports and certificates does.
Third, TR19 Grease is not written that way. The specification works on measured deposit and planned frequency precisely because visual judgement is unreliable. If you want to understand what the resulting paperwork should contain, see what is in a TR19 report.
The practical approach is to establish your band honestly (count actual cooking hours, not opening hours), adjust for cooking style and system layout, and put the resulting interval in the diary as a planned maintenance item alongside your other ventilation obligations, such as fire damper testing and general ductwork cleaning. Each clean then resets the clock and adds a report and certificate to your fire safety records.
As a BESCA Vent Hygiene Associate member, our operatives are TR19 trained and our work is independently audited, so the certificate you file after each visit is verified rather than self-declared.
If you are not sure which band your kitchen falls into, or when the system was last cleaned along its full length, book a free survey through our contact page or request a TR19 quote. If you have an existing TR19 report from a previous contractor, send it over and we will read it and tell you where you stand.
TR19 Grease links frequency to daily cooking hours. Heavy use of 12-16 hours a day calls for a clean every 3 months, moderate use of 6-12 hours every 6 months, and light use of 2-6 hours every 12 months. These are baseline intervals, and factors such as solid-fuel cooking or heavy frying can justify cleaning more often.
Yes. Charcoal grills, wood-fired ovens and similar equipment add combustion products to the grease load and cause deposits to build faster than the daily-hours band alone suggests. Kitchens using solid fuel are widely treated as needing more frequent extract cleaning, and a survey should confirm the right interval for the specific system.
No, and for a practical reason: the risk is invisible. The grease that carries a fire sits inside the ductwork between the canopy and the fan, where nobody looks during normal operation. Visual judgement also produces no documentary evidence, which is what your fire risk assessor and insurer will ask for. A planned schedule based on TR19 Grease usage bands, with reports and certificates after each clean, is the defensible approach.
No. The TR19 Grease bands are based on actual cooking time, the hours the equipment under the canopy is genuinely in use, not the hours the premises are open. A restaurant open twelve hours a day but cooking for eight sits in the moderate band. Count honestly, because an interval built on the wrong band leaves the system overloaded between cleans.
Send us your existing report or book a free survey. A named engineer replies within 24 hours.