Signs & diagnostics
A kitchen can look spotless at the cookline and still carry a heavy grease load overhead. These are the six signals that say the extract ductwork - not just the surfaces - needs a professional clean.
The short answer
Grease-laden vapour rises off the cookline every service and settles inside the canopy, filters, ductwork and fan long before it becomes obvious to the eye. By the time you can see it, the internal contamination is usually well advanced. The six signs below are the everyday cues that the hidden part of the system has fallen behind - a lingering smell, grease at the canopy, smoke that will not clear, a fan that sounds strained, greasy surfaces spreading, and creeping heat or energy use. Any one of them is worth a look; several together mean the duct is overdue.
Why the visible clues matter
The reason these signs matter is that the dangerous grease is the grease you cannot see. Wiping the outside of a canopy improves how it looks but does nothing for the ductwork, the fan housing or the concealed runs above the ceiling where deposits build up unchecked. Under the BESA TR19 Grease specification, grease is meant to be controlled so it does not exceed a mean average of two hundred microns between cleans - about half the thickness of a business card - with any single point of five hundred microns or more needing immediate spot cleaning.
That is why the everyday signs are useful. You are not measuring microns at the cookline, but a smell that returns after cleaning, or smoke that hangs longer than it used to, is the system telling you the concealed surfaces have loaded up. The signs are the prompt; a survey and deposit measurement turn the prompt into a decision.
Reading the six signals together
Taken alone, a single sign can have an innocent explanation: a busy night, a filter due a change, a warm day. What matters is the pattern. When the smell, the smoke and the fan noise all shift in the same direction over a few weeks, that is grease narrowing the free area of the duct and loading the fan - not a one-off. The value of knowing the six is that you stop treating them as separate annoyances and start reading them as one system falling behind.
The practical move is to note when each sign started and whether it is getting worse. A system that was cleaned three months ago and is already showing two or three signs is telling you the interval is too long for how hard the kitchen is working - and that is exactly the judgement a cleanliness risk assessment is meant to make.
What to do about it
The six signs are a prompt to inspect, not a diagnosis on their own. A proper survey opens the access panels, measures grease deposits along the run and tells you where the system stands against the TR19 Grease benchmarks - so cleaning is scheduled on evidence rather than guesswork. If several of these signs are present, the sensible next step is to have the ductwork looked at before the grease load climbs any further.
Questions
Any single sign is worth investigating, but two or more appearing together over a few weeks is a strong signal that the ductwork has fallen behind and should be surveyed. The signs point to hidden grease; a survey and deposit measurement confirm how much.
You can spot the everyday signs, but you cannot measure the concealed duct surfaces by eye. TR19 Grease works to a mean average of two hundred microns between cleans, verified by a deposit thickness or wet film test - that measurement needs a competent technician and access to the run.
Yes. A spotless canopy at eye level tells you nothing about the ductwork, fan housing and concealed runs above the ceiling, which is exactly where grease builds up unseen. The visible steel is the easiest part to clean and the least useful guide to the hidden risk.
TR19 Grease gives indicative intervals by use - heavy kitchens running twelve to sixteen hours a day around every three months, moderate use around six, light use around twelve - but these are starting points. A cleanliness risk assessment by a competent person sets the real schedule for your kitchen.
Grease keeps accumulating, the fire risk rises, airflow and capture drop, and the fan works harder and wears faster. There is also an insurance dimension: if a fire is linked to inadequate cleaning, cover can be jeopardised. The signs are an early, cheap warning worth acting on.
Phoenix Duct Clean · by the numbers
If any of these signs sound familiar, a survey settles it. We inspect the run, measure the grease and tell you plainly whether it needs cleaning now.