Signs & diagnostics
When grease starts appearing at the canopy edge or dripping onto the cookline, the system has stopped containing it. By the time it is visible below, the ductwork above is almost certainly heavily loaded.
The short answer
A canopy and its filters are designed to catch grease-laden vapour and drain it back into the grease management system, not let it escape. So when grease starts collecting at the canopy edge, running down the outside, or dripping onto the cookline, it means that containment has broken down - the filters are saturated and grease is getting past them. It is a late-stage signal, not an early warning. When grease is visible below the canopy, the ductwork above it is almost always carrying a far heavier load than the drip suggests.
Why the drip understates the problem
The grease you can see dripping is the small fraction that has overflowed the system's capacity to hold it. Everything upstream - the filters, the canopy plenum, the ductwork and the fan - has already filled to the point where it is spilling over. In other words, the drip is the overflow from a system that is already full, so the concealed surfaces are in worse condition than the visible one.
This is why external grease is treated as a serious signal rather than a cosmetic one. Under TR19 Grease, deposits are meant to be kept to a mean average of two hundred microns, with anything at five hundred microns or more needing immediate spot cleaning. A canopy that is actively dripping is well past the point where a measurement would have flagged the system for cleaning.
What the drip tells you about the run
A dripping canopy is not an isolated fault - it reflects the state of the whole extract route. The same grease-laden vapour that overwhelmed the filters travels on into the ductwork, coating the internal surfaces, collecting in bends and rises, and eventually loading the fan at the end of the run. So the drip at the canopy edge is a visible symptom of an invisible condition that extends the full length of the system.
There is a hygiene and safety dimension too. Grease dripping onto the cookline or nearby surfaces spreads contamination, creates slip hazards and, most importantly, means the combustible load inside the duct has grown to the point where the fire risk is climbing. The drip is the cue to act on the concealed ductwork, not just to wipe the edge.
What to do about it
Wiping the canopy edge deals with the symptom and leaves the cause untouched. When grease is dripping, the right response is to survey the whole extract route - filters, plenum, ductwork and fan - measure the deposits against the TR19 Grease benchmarks and clean the parts that carry the risk. Because the drip signals an advanced load, this is usually a prompt for a full clean rather than a spot job.
Questions
It is not a fire in progress, but it is an advanced signal that should not wait. Active dripping means the system is past the point where routine measurement would have flagged it for cleaning, so the sensible response is to survey and clean promptly rather than schedule it for later.
Water or condensation can drip too, but greasy, sticky or discoloured drips are grease overflowing the system. If the residue feels tacky or leaves a film, it is grease - and that points to saturated filters and a loaded duct, not a moisture issue.
Cleaning or exchanging saturated filters helps, but it treats one stage of a system that is already full. If grease has reached the point of dripping, the ductwork and fan behind the filters are also loaded, so filter cleaning alone leaves the main risk in place.
There is no fixed ratio, but the principle holds: the visible drip is the overflow, so the concealed surfaces are always in worse condition than the part you can see. Only a survey with deposit measurement along the run tells you how much worse.
It can. Insurers expect kitchen extract systems to be maintained to a recognised standard, and visible grease is evidence the system has been allowed to fall behind. If a fire were linked to inadequate cleaning, that evidence could count against a claim - another reason to act on the signal.
Phoenix Duct Clean · by the numbers
Visible grease is a late signal. Let us survey the ductwork above before the load climbs - we will measure the deposits and tell you where the system really stands.