Three duct types
Grease is the one duct type with a defined cadence - a use-based matrix of roughly 3, 6 or 12 months. Here's why, and how to place your kitchen in its band.
The short answer
Kitchen grease-extract ductwork is cleaned to TR19 Grease on a use-based matrix: roughly every three months for heavy use, six months for moderate, and at least every twelve for light use. Grease is the only one of the three duct types with a defined cadence like this - because its hazard scales predictably with how hard the kitchen works.
The matrix
TR19 Grease bands a kitchen by how many hours a day it cooks and how heavy that cooking is. Heavy use - long hours, high-volume frying, roughly twelve to sixteen hours a day - points to cleaning about every three months. Moderate use of six to twelve hours a day points to six-monthly. Light use of two to six hours a day points to at least annually. The heavier and longer the cooking, the faster the combustible film builds, and the more often the system needs clearing.
Crucially, the interval applies to the whole run - canopy, filters, the ductwork, the fan and the discharge - not just the visible parts. A canopy wiped daily is good housekeeping, but it is not the TR19 clean the interval is counting.
Why grease gets a matrix
Grease is unusual among the duct types in that its risk grows in step with a measurable input - cooking. That predictability is exactly what lets a use-based table work: two kitchens running the same hours at the same intensity accumulate grease at broadly the same rate, so a shared schedule fits both. Dry ventilation and laundry ductwork do not have this - their contamination depends on far more variable factors, which is why they are cleaned on a risk-assessed basis rather than a fixed band.
That is the honest reason grease ductwork has a matrix and the others do not. It is not that grease matters more; it is that the grease hazard is regular enough to schedule against with confidence.
Getting your band right
Place your kitchen honestly in its use band and set the clean to match. Then check your insurance - a policy can stipulate a stricter interval than the matrix floor, and where it does, the policy wins. Keep dated certificates at whichever interval is more frequent, so you can always show the cadence was met. If you are unsure which band you fall into, the safe move is to assess against the heavier of the two you are between rather than the lighter.
The frequency question for grease ductwork, then, has a clear answer - which is precisely what makes it different from the other two duct types, where the honest answer is always "it depends on the risk."
Questions
To TR19 Grease on a use-based matrix: roughly every three months for heavy use, six months for moderate use, and at least every twelve months for light use - across the whole run from canopy to fan.
How many hours a day the kitchen cooks and how heavy that cooking is. Heavy use of twelve to sixteen hours points to quarterly, moderate six to twelve hours to six-monthly, and light two to six hours to annual.
Because the grease hazard grows predictably with cooking hours, a use-based table works. Dry ventilation and laundry ductwork depend on more variable factors, so they are cleaned on a risk-assessed basis instead.
Yes. It applies to the canopy, filters, ductwork, fan and discharge - not just the visible canopy. A daily canopy wipe is good housekeeping but is not the TR19 clean the interval counts.
The policy wins. If your insurer stipulates a stricter interval than the matrix floor, clean to that and keep dated certificates at whichever interval is more frequent.
Phoenix Duct Clean · by the numbers
We place your kitchen in its use band, schedule a TR19 Grease clean to match and certify every visit. Book an assessment today.