Compliance & responsibility
How often you clean the extract system is not a guess - it is a function of how hard the kitchen cooks. Here is the volume table and what moves you up it.
The short answer
The single biggest factor in how often a kitchen extract system needs cleaning is how much cooking it does. TR19 Grease captures this as three usage bands by daily operating hours. Heavy use - roughly twelve to sixteen hours a day - points to cleaning about every three months. Moderate use at six to twelve hours a day points to about every six months. Light use at two to six hours a day points to about every twelve months. These are the benchmark minimums the whole industry works from, and where most kitchens should start.
What moves you within a band
Two kitchens open the same hours can accumulate grease at very different rates, which is why cooking volume means more than the clock. High-grease cooking - char-grilling, wok work, heavy frying, solid-fuel and flame - loads the ductwork far faster than steaming, boiling or light service, and can push a kitchen toward a shorter interval than its hours alone suggest. Menu changes, seasonal peaks and a switch to a greasier service all shift the real requirement.
This is why TR19 treats the usage bands as minimums and hands the final decision to a competent person's cleanliness risk assessment. That assessment looks at the cooking processes, the food type, the hours and the grease the system genuinely carries, then sets an interval that keeps the system safe rather than merely on-category. A hard-frying unit open eight hours a day may sit in the moderate band on paper but need heavy-band frequency in practice.
The interval exists to hold a threshold
The frequencies are a means to an end, and the end is a grease level. Mean grease across the whole system must stay below 200µm between cleans - about half the thickness of a business card. Any single reading of 500µm or more calls for immediate localised cleaning of that spot, whatever the schedule says. After a clean, surfaces must verify below 50µm by Deposit Thickness Test or Wet Film Thickness Test. The right frequency is simply whatever keeps your system inside those limits.
Get the band wrong and the readings tell on you. Stretch a heavy kitchen to a moderate interval and the grease carbonises, the mean climbs over 200µm between visits, and each clean takes longer and costs more while leaving you technically non-compliant in the gap. Setting frequency from genuine volume rather than optimism is what keeps the microns - and the compliance - where they should be.
Placing your kitchen
The reliable way to fix your frequency is to have the kitchen surveyed rather than guessed. A short assessment weighs your hours, your cooking type and the grease the system carries, places you on the volume table, and sets a cleaning schedule that holds the system below the thresholds - with a certificate at each visit to prove the interval was met.
Questions
TR19 Grease bands kitchens by daily hours: heavy use (12-16h) about every 3 months, moderate (6-12h) about every 6 months, light (2-6h) about every 12 months. Those are minimums that the cooking type can shorten.
Yes. Char-grilling, wok work and heavy frying load the ductwork far faster than steaming or light service, so a kitchen can need a shorter interval than its hours alone suggest.
They are benchmark minimums. The final interval comes from a competent person's cleanliness risk assessment, which weighs cooking type, menu and the grease the system actually accumulates.
Mean grease below 200µm across the system between cleans, no single reading at or above 500µm, and surfaces verified below 50µm after a clean. The frequency is whatever keeps you inside those limits.
Grease carbonises and the mean climbs over 200µm between visits, leaving you non-compliant in the gap and making each clean longer and more costly. It is usually a false economy.
Phoenix Duct Clean · by the numbers
A quick survey places your kitchen on the volume table and sets the frequency that keeps you compliant.