The five parts of the system
Grease filters. Baffle or mesh panels in the canopy that force extracted air to change direction so grease drops out. They are removable and are the only part of the system the kitchen team cleans routinely.
Canopy and plenum. The hood over the cooking line, its grease trays and the chamber above the filters where the duct begins. Grease that passes the filters lands here first.
Ductwork. The run from the plenum to the discharge point, often through ceiling voids, risers and other tenants' space. Grease condenses on its walls and is invisible from the kitchen. DW172, the design specification, expects access panels at intervals along the run and wherever the duct changes direction.
Extract fan. The impeller and casing, plus any attenuator or flexible connection. Grease on the impeller unbalances it, cuts airflow and puts the motor next to the fuel.
Grease trap or separator. Not part of the airflow, but part of the same grease problem. It sits on the drain line and stops fats, oils and grease reaching the sewer.
The schedule by kitchen type
Frequencies for ductwork and fans follow the BESA TR19 Grease minimums, which are set by daily cooking hours. Filter and canopy frequencies are working practice from fire service guidance and the food hygiene inspection regime.
| Kitchen type | Cooking hours | Filters | Canopy and trays | Ductwork and fan (TR19 Grease) | Grease trap |
|---|---|---|---|---|---|
| Hotel, contract catering, high-volume restaurant, chargrill or fryer-led menu | 12 to 16 hours a day | Twice weekly or more | Weekly | Every 3 months | When a quarter full, often monthly |
| Standard restaurant, gastropub, busy cafe, staff canteen | 6 to 12 hours a day | Weekly | Fortnightly | Every 6 months | Every 1 to 3 months |
| Cafe, school, care home, small pub kitchen, office pantry with cooking | 2 to 6 hours a day | Weekly | Monthly | Every 12 months | Every 3 months or when a quarter full |
Three adjustments to make before you fix the schedule.
- Cooking style outranks hours. Solid-fuel and charcoal grills, woks and open fryers load ductwork far faster than steam ovens and induction. A grill house open eight hours a day belongs in the heavy row.
- Readings outrank the table. If the last TR19 Grease report showed pre-clean readings near the 200 micron mean limit, or any point above 500 microns, shorten the duct interval. If readings came back low after a full interval, keep the interval, do not stretch it.
- Shared ducts take the strictest tenant's interval. Where several kitchens discharge through one riser, the landlord's schedule should be driven by the heaviest user.
What each task involves
Filters. Remove, wash in the dishwasher or a degreasing tank, dry, refit. Replace panels with missing baffles or split mesh. Never run the system with filters out. Record the wash in the cleaning diary.
Canopy and trays. Empty and degrease the trays. Degrease the canopy face, underside, filter housings and light covers. Shine a torch into the plenum. If grease is visible on the plenum walls or duct entry, bring the next TR19 Grease visit forward.
Ductwork and fan. Specialist work done out of hours. The contractor takes wet film thickness readings and photographs at each access point, scrapes and degreases every reachable run, cleans the fan impeller and casing, then repeats the readings and photographs. Anything unreachable is recorded and, with the client's agreement, new access panels are fitted.
Grease trap. Emptied by a licensed waste carrier once fats fill about a quarter of the trap, with the waste transfer note kept on file. Enzyme dosing does not remove the need to empty the trap.
Signs the schedule is too long
- Grease dripping from the canopy edge or filter housings during service.
- A film of grease on the wall or roof around the discharge point.
- Reduced draw at the canopy, smoke drifting into the kitchen, fire alarms triggering on cooking.
- Grease visible at duct joints or on the fan casing.
- Odour complaints from neighbours or from other tenants sharing the riser.
- Pre-clean readings on the last report close to the 200 micron mean or any point above 500 microns.
Any of these means the next TR19 Grease clean is due now, whatever the calendar says.
What a good report looks like
The report is the evidence you hold for the fire risk assessment, the insurer, the landlord and the Environmental Health Officer. Two reports are involved.
Canopy and filter cleaning belongs in the kitchen's cleaning schedule and diary under the Safer Food Better Business approach. Date, task, who did it, initials. A deep clean contractor adds before and after photographs by area.
Ductwork and fan cleaning needs a TR19 Grease post-clean verification report. The four things to check before you file it: micron readings before and after at every access point with the mean; a before and after photograph at every access point, not one composite image; a schematic marking the access points; and a plain statement of any section not cleaned and why. The full contents of a compliant report are set out in our TR19 Grease guide.
A report missing the micron readings or the schematic should be sent back. A statement that the system "was cleaned to TR19" with no numbers is not a verification report.
File every report with the fire risk assessment, keep the cleaning diary for the food hygiene inspection, and give the landlord or managing agent a copy of each TR19 Grease report.
How Commercial Cleaning London arranges it
Commercial Cleaning London sets the schedule with you from the table above, adjusted for menu and readings, and writes it into a single specification covering filters, canopy, ductwork, fan and grease trap. The kitchen team keeps the weekly tasks and diary. The extract clean is carried out by an appointed TR19 Grease specialist and grease trap waste goes through a registered carrier, both scheduled out of hours, with their reports passed to you. We hold the next-due date for each item against the TR19 Grease interval for your hours-of-use category and confirm the booking before it lapses.