Signs & diagnostics
Grease on the canopy edge is the part of the story you can see - and it is the last chapter, not the first. By the time it shows on the lip, the filters and duct behind it are usually well loaded, which makes a visible edge a reliable prompt to measure and clean rather than a small job to wipe.
The short answer
Grease on the canopy edge is the part of the story you can see - and it is the last chapter, not the first. By the time it shows on the lip, the filters and duct behind it are usually well loaded, which makes a visible edge a reliable prompt to measure and clean rather than a small job to wipe.
The detail
Grease enters the system as an aerosol in the plume and is meant to be caught by the baffle filters, which spin it out by forcing the air to change direction. What the filters miss travels on into the plenum and duct. The canopy lip is downstream of all of that in visible terms - it only shows grease once the system upstream is saturated enough to shed it back.
That is why experienced contractors read a visible lip as advanced contamination. The clean stainless you can polish is the least of it; the fire fuel and the airflow restriction sit inside the duct where you cannot see them without a borescope.
The visible grease and the hidden buildup are the same problem. The coating that shows at the edge is also raising resistance across the filters and duct, cutting the airflow the fan can move and lowering capture at the canopy face - so the eyesore and the performance loss share a cause.
Wiping the lip treats the symptom and hides the warning. The stainless looks fine again, but the loaded duct behind it keeps building, and the next outward sign is often grease dripping or a smell rather than a tidy edge - by which point more of the system needs attention.
What it means for you
The right response to a visible lip is to measure, not to guess. A WFTT or DTT taken at set points tells you where the system sits against the TR19 Grease thresholds - a mean of 200 microns, a 500 micron point that demands immediate cleaning, and the high-risk band beyond 1,000 microns.
Access panels roughly every two metres let a technician inspect and measure the runs you cannot see, which is where the real story is. A visible edge plus interior readings turns a vague worry into a clear decision about scope and urgency.
Phoenix Duct Clean inspects, measures and cleans the full path back below the verification threshold, then documents it with before and after photos and readings - so a warning sign becomes a proven-clean, evidenced system.
The service behind the guide
Sibling guides
Filters that won't come clean · Why the fan trips under load · Cafe extraction cleaning
Questions
Usually yes, because the edge shows grease last. A small amount visible on the lip generally means the filters and duct upstream are already well loaded. It is the tip of the buildup, not the whole of it, so it warrants an inspection with readings.
Wiping keeps the stainless tidy but does nothing about the loaded duct behind it, which is where the fire risk and airflow loss sit. The grease will re-appear because its source is internal. Only a full clean addresses the cause.
By measuring it. A borescope inspection plus WFTT or DTT readings at set points shows the grease thickness through the system against the TR19 thresholds, so you know whether you need a spot clean or a full one and how urgently.
TR19 Grease sets a mean cap of 200 microns, requires immediate localised cleaning at any single 500 micron reading, and industry banding treats 1,000 microns or more as a high fire risk. Post-clean, deposits should verify below 50 microns.
Because the grease that matters is inside the duct where you cannot see it. Access panels roughly every two metres let a technician inspect, measure and clean the hidden runs. Without them, a proper assessment of the warning is impossible.
Phoenix Duct Clean · by the numbers
Treat it as a measure-and-clean prompt. Book an inspection with grease readings today.