Signs & diagnostics
Five symptoms flag an extract that is overdue a clean before any calendar does: smoke that will not clear, weaker pull at the canopy, grease showing where it should not, a fan that sounds like it is labouring, and a kitchen that runs hot. Every one of them traces back to grease.
The short answer
Five symptoms flag an extract that is overdue a clean before any calendar does: smoke that will not clear, weaker pull at the canopy, grease showing where it should not, a fan that sounds like it is labouring, and a kitchen that runs hot. Every one of them traces back to grease.
The detail
The first sign is smoke and steam that hang in the room during service instead of leaving through the canopy. When capture is healthy the plume is drawn away at source. When it lingers, the extract is no longer holding the airflow it was commissioned to move, and grease is the usual reason.
The second and third are visible: grease drips or beading at the filters and canopy lip, and sticky, darkening patches on nearby walls and ceilings. Grease only escapes back into the room once the filters and duct are loaded, so surface staining means the inside is already well coated.
The fourth is sound. A fan that has picked up a new rattle, hum or vibration is usually working against extra resistance or carrying grease on its impeller, which throws it out of balance. The fifth is heat: a kitchen creeping hotter through the year as the extract quietly loses capacity.
None of these are cosmetic. Each is the visible end of the same chain - grease loads the baffle filters, then the plenum, duct and fan; static pressure climbs; the fan moves less air; capture velocity at the canopy face drops. The symptom in the room is the system telling you its airflow has fallen.
What it means for you
TR19 Grease asks that grease is kept to a mean of 200 microns between cleans, with any single reading of 500 microns or more triggering immediate localised cleaning. You cannot see microns, but you can see and hear the symptoms above - and they tend to appear as readings climb toward those thresholds.
The catch is that grease shows at the canopy edge last, not first. By the time it is visible on the lip, the inside of the duct is usually well advanced. So a visible sign is rarely early - it is a prompt to measure and act, not to wait for the next scheduled visit.
Phoenix Duct Clean inspects with a borescope, measures grease at set points with a WFTT or DTT, cleans the full system back to TR19 Grease condition and leaves before and after photos and readings. That is the difference between guessing from the symptoms and knowing where you stand.
The service behind the guide
Sibling guides
Grease dripping from the canopy · Why smoke hangs around at service · Takeaway extraction cleaning
Questions
One is enough. Lingering smoke, grease drips, a labouring fan, sticky surfaces or a hotter kitchen each indicate the extract has lost capacity. They rarely appear early, so treat any of them as a prompt to inspect and measure rather than a reason to wait.
They can. A fan fault, an undersized system or a poorly positioned canopy produce similar symptoms. A proper inspection with grease measurement tells you whether cleaning will fix it or whether the system has a separate mechanical or design issue.
With a Wet Film Thickness Test for softer grease or a Deposit Thickness Test for harder carbonised deposits, taken at set points along the system. TR19 Grease sets a mean cap of 200 microns and a 500 micron point that demands immediate cleaning.
If grease is the cause, yes - restoring the system to TR19 condition brings back the design airflow, so capture, noise, heat and staining all improve. If a sign persists afterwards, that points to a mechanical or design fault to diagnose separately.
TR19 Grease baselines are three months for heavy use, six for moderate and twelve for light, but the real interval comes from a competent person's cleanliness risk assessment based on how much grease your cooking produces.
Phoenix Duct Clean · by the numbers
Book a TR19 Grease inspection and clean and get the airflow and capture back.