Renovation dust is not household dust. Hacking, plastering, tile cutting and carpentry throw out fine cement and gypsum particles that stay airborne for hours and settle into every gap in the flat — including the inside of an air conditioner that was sitting there switched off with its cover on. Owners are often surprised by this. The unit was closed. Nobody used it. How did it get dirty?
It got dirty because a wall-mounted fan coil is not sealed. It has a large open return above the filter, a drain line into the wall, and a gap behind the casing where the pipe chase runs. Dust does not need the unit to be running to get in. It only needs time, and a renovation gives it weeks.
This is what renovation dust actually does to an aircon, how to tell whether a general service will clear it or whether the unit has gone past that, and when in the schedule to book the visit so you are not paying twice.
Why the filter is the least of it
Most people check the filter, see a grey mat of dust, wash it, and assume that was the problem. The filter is doing its job when it looks like that. The question is what got past it, and during a renovation a great deal does — partly because the particles are finer than household dust, and partly because the filter is usually already loaded before anyone thinks to check.
Three places take the damage:
- The blower wheel. This is the long barrel-shaped fan inside the unit, and it is the single worst place for renovation dust to settle. Cement dust sticks to the slightly damp blades and hardens. Once each blade carries a rim of set dust, the wheel moves less air, the unit runs longer to hit the same temperature, and the noise changes — usually a low hum or a rattle that was not there before.
- The coil fins. The evaporator coil is a dense stack of thin aluminium fins with very little space between them. Fine dust bridges across those gaps and blocks airflow through the coil, which is why a flat that has just been renovated often feels like the aircon is "not as cold as before" even though nothing is broken.
- The drain pan and drain line. Dust that lands on a wet coil washes down into the drain pan as sludge. Cement dust in particular sets. A partially blocked drain does not announce itself immediately — it shows up weeks later as water dripping from the front edge of the unit onto the new flooring you just paid for.
None of those three are reachable by washing a filter. That is the whole reason a post-renovation service is a different conversation from a routine one.
Which trades cause the worst of it
If you want to know how bad the load is likely to be, look at what was actually done in the flat rather than how long the works took:
- Hacking and tile removal produce the heaviest and most abrasive dust of any renovation stage. If walls or floor tiles came off, assume the units are loaded.
- Plastering and skim coat produce very fine gypsum dust that travels furthest through the flat and settles most evenly. This is the dust that reaches bedrooms nobody worked in.
- Tile cutting, especially dry cutting indoors, throws a dense plume in a short burst. One afternoon of it can do more than a week of general works.
- Carpentry and sanding give you sawdust, which is coarser and largely caught by the filter — the least damaging of the four, though it clogs filters fast.
- Painting is mostly harmless to the internals, but overspray on the casing and louvres is common and does not always come off easily later.
A flat that had a full hack-and-rebuild is a different case from a flat that had carpentry and a repaint. Be honest with whoever you book about which one it was — it changes what they should quote you.
What to do while the works are still running
The cheapest post-renovation service is the one you partly avoid. Three things help, and all of them are free:
- Keep the units off. A running unit actively pulls dust-laden air across the coil and into the blower. This is the single biggest difference between a unit that needs a wipe and a unit that needs a wash.
- Bag or wrap the indoor units before dusty stages, and tell the renovation contractor you want it done. Cling wrap or a plastic sheet taped around the casing costs nothing and keeps the bulk of the settled dust off the return. Take it off before you switch anything on.
- Do not let anyone run the aircon "to clear the smell" during painting or after solvent-based works. It does not clear anything and it draws the fumes and particles straight through the coil.
If the units were newly installed as part of the renovation, ask the installer to leave the protective wrapping on until handover. Most will if asked, and few offer.
General service or chemical wash?
After a renovation this is the only decision that really matters, and it comes down to whether the dust is still loose or has already set.
A general service — filter clean, coil wipe, drainage flush and gas check — is enough when the works were light, the units stayed off and wrapped, and the flat was mainly carpentry and paint. It is also the right first step if you genuinely do not know: a technician who opens the unit can see the blower wheel and tell you what is there.
A chemical wash is the honest answer when the flat was hacked, when the units were run during the works, or when the blower blades already carry a hardened rim. A wash treats the coil and blower with chemical solution rather than wiping them, which is the only way to shift set cement dust without stripping the unit down.
Our prices are published in full and the displayed price is the final price. General service is $45 for one unit, $70 for two, $95 for three, $115 for four, and $25 per unit from five up. Chemical wash is $135 for one unit, $245 for two, $345 for three, $425 for four, and $100 per unit from five up. The full list, including chemical overhaul, is on the pricing page.
Every booking includes a 9-point pre-check, which is the part that matters here: it tells you whether cleaning will actually fix the complaint before you have paid for cleaning. After a renovation that is worth having, because "not cold enough" can be a blocked coil or it can be something the works disturbed — and those have very different bills.
When to book it
Book the service after the last dusty trade has finished and before you move in. That is a narrow window and it is easy to miss, because the natural instinct is to service the aircon once you have settled in and noticed it is weak.
Doing it before you move in is better for two reasons. The technician can work without moving your furniture, which makes the job faster and cleaner. And more importantly, you avoid running a dust-loaded unit for a month, which is exactly how a general service turns into a chemical wash.
If final cleaning is being done by a cleaning company, book the aircon service after them, not before. General cleaning disturbs settled dust and puts a fresh load back into the air.
If the units were installed during the renovation
New units still get dirty — sometimes worse than old ones, because they go in before the works are finished and then sit through the dusty stages. But there is one thing to settle before you pay anyone for cleaning them.
Check the installation warranty and the equipment warranty separately. They cover different failures. If a brand-new unit is dripping, running weak or noisy within weeks of the works, that may be an installation matter for whoever fitted it rather than a cleaning matter — a drain gradient set wrong, or piping disturbed by another trade. Servicing it yourself first can muddy that conversation. More on what to ask before a new install is in our guide to budgeting and asking the right questions for a new BTO installation.
The short version
Renovation dust reaches parts of an aircon a filter clean does not touch. Keep the units off and wrapped while the works run, book the service after the last dusty trade and before you move in, and expect a chemical wash rather than a general service if the flat was hacked or the units were left running. If you are not sure which you need, book the general service and let the pre-check tell you — it is the cheaper way to find out.
Related reading: the signs that a unit needs a chemical wash rather than a general service, why an aircon starts leaking water and how to stop it, and the best and worst times to service an aircon in Singapore.
Book a post-renovation service
Tell us what was done in the flat and how many units there are, and we will tell you whether a general service will clear it. Message us on WhatsApp, or see aircon servicing and chemical wash for what each visit covers.