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Extraction cleaning - reading the signs
Grease marks spreading on the ceiling near the kitchen are a sign worth taking seriously, because of where the grease is coming from. It is not settling from the air - it is escaping the ductwork running above the ceiling, leaking out of joints and seams as the ducts load with grease. Ceiling grease marks are the sign of a duct problem happening out of sight. Here is what they are telling you.
The short answer
Grease marks on the ceiling near a kitchen usually mean grease is leaking out of the extraction ductwork that runs above the ceiling. As grease builds up inside the ducts, it can find its way out through the joints and seams of the ductwork - places where sections join, where the duct is not perfectly sealed - and where the ducts run above a ceiling, that escaping grease marks the ceiling from above, showing as stains spreading on the ceiling surface. So the marks are a sign that the ductwork above is loaded with grease and leaking, which is a problem happening out of sight. It points to a duct that needs cleaning - and possibly to joints that need attention - because a duct leaking grease is both a heavily loaded fire risk and a sign the system is not sealed as it should be. Ceiling grease marks are worth acting on, not painting over.
The grease is coming from above
The first thing to understand about grease marks on the ceiling is where the grease is coming from - because it changes what the marks mean. It is tempting to assume the grease is settling from the greasy kitchen air onto the ceiling, but marks that spread and stain the ceiling, particularly along lines or around fixings, usually indicate something different: grease escaping from the extraction ductwork that runs in the ceiling void above. The ducts carry the greasy extracted air across the building, often above ceilings, and when they load with grease and leak, the grease comes out above the ceiling and marks it from that side. So the marks are coming from the duct above, not settling from the air below.
This matters because grease leaking from the ductwork is a more serious sign than grease settling from the air. Grease settling from the air points to the extraction under-capturing; grease leaking from the duct points to the duct being so loaded that grease is escaping it, and to the duct not being sealed as it should be. The pattern of the marks often gives it away - stains following the line of the duct above, or concentrated around joints and fixings, rather than a general film - showing the grease is tracking out of the ductwork and through the ceiling. So reading ceiling grease marks starts with recognising that the grease is coming from the duct above, which makes them a sign of a duct problem, out of sight in the ceiling void.
How grease escapes the duct
For grease to be leaking from the ductwork, two things are usually going on: the duct is heavily loaded with grease, and it has points where the grease can escape. As grease accumulates inside the ducts, it builds up as a thick, and in warm conditions semi-liquid, layer lining the duct. Ductwork is made of sections joined together, with joints and seams where the sections meet, and these are the weak points: if they are not perfectly sealed - and over time, or with a heavy grease load, they often are not - grease can seep out through them. So the escaping grease finds its way out at the joints and seams, driven by the sheer quantity of grease inside and by any imperfection in the sealing.
The heavier the grease loading, the more grease there is to escape and the more likely it is to find its way out - so leaking from the joints tends to happen when the duct has become significantly loaded. Warmth makes it worse, as grease softens and flows more readily when the system is running and hot. So a duct that is leaking grease onto the ceiling is typically one that has loaded up heavily, to the point where the accumulated grease is escaping through the joints. That is why the marks are a sign of a loaded duct: the leaking is a consequence of the build-up reaching a level where the grease is escaping the ductwork. Reading the marks means reading a heavily loaded, leaking duct above the ceiling.
Why it matters
Grease marks on the ceiling matter for two connected reasons. First, they indicate the ductwork above is heavily loaded with grease - loaded enough to be leaking - which means the fire risk in that duct is significant. A duct leaking grease is a duct lined with a heavy layer of combustible grease, exactly the build-up that is a fire hazard and that a professional clean exists to remove. So the marks are, indirectly, a fire-risk sign: they are telling you the duct above the ceiling has loaded to a serious level. That is the more important of the two reasons, and the one that makes the marks worth acting on promptly rather than ignoring.
Second, grease escaping into the ceiling void is a problem in itself, beyond the fire risk in the duct. Grease leaking out of the ductwork means grease is getting into the ceiling void - the concealed space above the ceiling - where it can spread, soak into materials, and create a fire risk in the void as well as in the duct. A grease-contaminated ceiling void is a hidden hazard, and the marks on the ceiling are the visible sign of it. So ceiling grease marks point to two things needing attention: the heavily loaded duct that needs cleaning, and the grease that has escaped into the void and the joints that let it out. Both are reasons to treat the marks as a real sign of a problem, not a cosmetic blemish to paint over - painting over them leaves the leaking, loaded duct above entirely unaddressed.
What to do about it
The right response to grease marks on the ceiling is to address the duct above, not just the marks. The marks are the visible sign; the problem is the loaded, leaking ductwork in the void. So the action is to have the ductwork professionally cleaned - removing the heavy grease build-up that is both the fire risk and the source of the leaking grease. Cleaning the duct takes away the accumulated grease, which addresses the fire risk and removes the grease that was escaping through the joints. That is the core of the response: clean the loaded duct that the marks are pointing to.
Alongside cleaning, the leak itself - the joints and seams that let the grease escape, and any grease that has got into the ceiling void - may need attention, because a duct that has been leaking may have sealing that needs addressing to stop it leaking again once cleaned. And it is worth understanding that ceiling grease marks usually indicate the duct is significantly loaded, so they are a prompt for cleaning that is arguably overdue - the leaking is a sign the build-up has gone quite far. So treat ceiling grease marks as a clear pointer to the ductwork: have the duct cleaned to remove the build-up and the fire risk, address the joints and any void contamination to stop the leak, and recognise that the marks appearing means the system has loaded to the point of leaking - a sign to act on. Painting over the marks without cleaning the duct leaves the real problem, loaded and leaking, above the fresh paint.
The takeaway
Grease marks on the ceiling near a kitchen usually mean grease is escaping the extraction ductwork running above the ceiling - leaking out through joints and seams as the ducts load with grease, and marking the ceiling from above. So the grease is coming from the duct above, not settling from the air below - which makes the marks a sign of a duct problem happening out of sight in the ceiling void. The leaking happens when the duct has loaded heavily, to the point where the accumulated grease is escaping through the joints, helped by warmth softening the grease.
That makes ceiling grease marks worth taking seriously. They indicate the duct above is heavily loaded - so the fire risk in it is significant - and that grease is escaping into the ceiling void, a hidden hazard in itself. The response is to address the duct, not just the marks: have the ductwork professionally cleaned to remove the build-up and the fire risk, and address the joints and any void contamination to stop the leak. And recognise that the marks appearing means the system has loaded to the point of leaking - a sign that cleaning is arguably overdue. So do not paint over ceiling grease marks: read them as the sign they are of a loaded, leaking duct above, and clean the duct they are pointing to.
Questions
Usually because grease is leaking out of the extraction ductwork running above the ceiling. As grease builds up inside the ducts, it escapes through the joints and seams, and where the ducts run above a ceiling, that escaping grease marks the ceiling from above. So the marks come from the loaded duct above, not from grease settling out of the air below.
Usually not, if the marks spread and stain rather than forming a general film. Marks that follow the line of the duct above, or concentrate around joints and fixings, indicate grease escaping the ductwork in the ceiling void - a more serious sign than grease settling from the air, because it points to a duct loaded enough to be leaking and not sealed as it should be.
Through the joints and seams where duct sections meet. As grease builds up inside the ducts as a thick, in warm conditions semi-liquid, layer, it can seep out through any joint that is not perfectly sealed - which, over time or under a heavy load, many are not. The heavier the loading and the warmer the running duct, the more grease escapes.
For two reasons. They indicate the duct above is heavily loaded - loaded enough to be leaking - so the fire risk in it is significant. And grease escaping into the ceiling void is a hidden hazard in itself, spreading and soaking into materials where it creates a fire risk in the void too. So the marks point to both a loaded duct needing cleaning and grease that has got into the void.
Address the duct above, not just the marks. Have the ductwork professionally cleaned to remove the heavy grease build-up that is both the fire risk and the source of the leak, and address the joints and any grease that has got into the ceiling void to stop it leaking again. Painting over the marks without cleaning the duct leaves the loaded, leaking duct entirely unaddressed.
Usually, yes. Grease only leaks from the ducts once the build-up has gone quite far - loaded to the point where the accumulated grease is escaping the joints. So ceiling grease marks appearing means the system has loaded to the point of leaking, which makes them a sign that cleaning is arguably overdue and should be acted on promptly.
Grease marks on the ceiling mean the duct above is loaded and leaking - our extraction cleaning removes the build-up that is the fire risk and the source of the leak, addressing the problem above the paint.
