Aircon Guide · Singapore · Updated July 2026
Aircon Smells Chemical After a Renovation?
The short answer: it is almost never the aircon making the smell — it is your new carpentry, paint and glue. But a dirty aircon can hold those fumes and hand them back every time you switch it on.
The 30-second version
- • New carpentry, paint and glue release fumes for months — this is the actual source.
- • Your aircon recirculates the same room air. It cools; it does not bring in fresh air.
- • Grime inside a dirty unit soaks up those fumes and releases them when the fan starts.
- • Cleaning the unit stops that burst. It does not stop the carpentry releasing more.
- • Ventilation and dealing with the source come first. Always.
Your aircon cools air — it does not replace it
This is the part most people get wrong, and it explains almost everything else. The wall-mounted unit in your bedroom has no fresh-air intake. It pulls room air in at the top, runs it over a cold coil, and blows the same air back out colder and drier. The outdoor unit is exchanging heat, not air.
So over eight hours in a closed bedroom, the same air goes through the unit again and again. Whatever your new wardrobe is releasing during those eight hours stays in the room with you. Running the aircon does not dilute it — opening a window does.
Why the smell hits hardest in the first minutes
When the aircon runs, the cooling coil sits well below room temperature and pulls moisture out of the air — that is the water draining out of the pipe outside. Many renovation fumes, formaldehyde especially, dissolve very readily into that film of water on the cold coil. At the same time, the layer of dust and grime coating the coil and the blower wheel acts like a sponge for them.
Then you switch the unit off. The coil dries out, and everything it absorbed slowly comes back off the surfaces. When you switch on again the next evening, the first rush of air carries a concentrated dose straight into the room — right when you have walked in and are most likely to notice it.
Worth being fair to the aircon here: a clean unit that drains properly does the opposite, slightly. Fumes that dissolve in the water and leave down the drain pipe are genuinely gone. The problem belongs to units carrying a thick layer of grime — the ones overdue for a wash.
Which smell do you actually have?
Homeowners often mix these up, and they need completely different fixes. The smell type and the timing tell you which one you are dealing with.
Musty, sour or damp — like an old towel
Mould and bacteria on the cooling coil and drain tray. This one really is the aircon.
Start with: Chemical wash — See the musty-smell guide →
Sharp, chemical or “new furniture” — eyes and nose sting
Formaldehyde and other fumes off-gassing from new carpentry, paint and adhesives. The aircon is carrying it, not creating it.
Start with: Ventilate, then test the air — How air testing works →
Chemical smell, but only in the first minutes after switching on
Fumes absorbed by the grime inside a dirty unit while it was off, released in a burst when the fan starts.
Start with: Chemical wash + ventilation — What a chemical wash covers →
Burning or electrical smell
Overheating wiring or a failing motor. Unrelated to renovation — switch off at the breaker.
Start with: Stop using it, get it checked — Aircon repair →
One important caveat: fumes like formaldehyde are largely odourless at the levels that matter most, and your nose stops noticing any smell within minutes of walking into a room. Stinging eyes, a scratchy throat, or a headache that eases when you leave the flat and returns when you come back is a more reliable signal than smell alone.
Does a chemical wash fix it? Partly — and here is the honest limit
What it does fix
- • Strips the grime holding fumes, so the burst on start-up stops
- • Removes renovation dust settled on the coil and blower wheel
- • Clears the mould and bacteria behind a musty smell
- • Restores airflow and cooling lost to a clogged coil
What it does not fix
- • The carpentry, paint and glue still releasing fumes
- • A room with no ventilation
- • Elevated readings anywhere else in the home
- • Anything you have not measured — cleaning is not testing
A chemical wash starts at $110 per unit — see what an aircon chemical wash includes. It is worth doing on its own merits if the unit is dirty or was running through the renovation dust. But if the air itself is the concern, cleaning the aircon is step four, not step one.
What to do, in order
Ventilate properly, every day
Windows open on opposite sides with a fan pushing air out, for as long as you can manage. Free, and the single most effective thing most households can do. Air the room out before closing it up for the night.
Deal with the source
The fumes come from composite-wood carpentry and they continue for months or years, not days. Where carpentry is already installed, professional treatment of the exposed surfaces is what reduces it at the origin.
Test if anyone vulnerable lives there
Since smell is unreliable in both directions, a proper reading is the only way to know where you stand. Especially worth it with a newborn, during pregnancy, or if someone in the home has asthma.
Clean the aircon
Removes the reservoir inside the unit and the renovation dust on the coil, so the aircon stops adding to the problem. Do it alongside the steps above, not instead of them.
If there is a baby in the home
The nursery is often the newest room in the flat — new cot, new wardrobe, new paint — and it is also the room with the door closed and the aircon running all night. Infants breathe roughly twice as much air per kilogram of body weight as adults do. That is a reason for care rather than alarm: air the room out daily, let new furniture off-gas before the room is occupied, have the aircon cleaned before the baby moves in, and get a reading if the renovation was recent.
Common questions
Does aircon servicing remove formaldehyde from my home?
No. Servicing or a chemical wash removes what has collected inside the unit, which stops the aircon giving the smell back every time it starts. It does not reduce what your new carpentry is releasing into the room — that keeps going regardless of how clean the aircon is. Anyone who tells you servicing solves a formaldehyde problem is selling you the wrong thing.
Why does my new flat smell worse when the aircon is on?
Two reasons. First, a closed, air-conditioned room has no fresh air coming in, so fumes build up instead of being diluted. Second, if the unit is dirty, the grime inside absorbs those fumes while the aircon is off and releases them in a burst when the fan starts — which is why the first few minutes are the strongest.
Should I keep the aircon off after a renovation?
Not necessarily. Cool, drier air actually slows how fast new carpentry releases fumes, so the aircon helps in that one respect. The mistake is treating a cool room as a fresh one. Air the room out properly first, then close up and run the aircon.
Will an air purifier in the aircon help?
The thin filters inside an aircon — including ones labelled deodorising, plasma or ion — are designed for dust and odour, not for fumes like formaldehyde. A separate purifier with a real weight of activated carbon can absorb some, but it needs replacing on schedule and it is no substitute for opening windows.
How soon after renovation should I service the aircon?
If the unit ran during the works, sooner rather than later. Renovation throws a lot of fine dust — cement, sawdust, paint particles — and a coat of that dust on the cooling coil is exactly what holds fumes and grows mould later. Many homeowners book a wash once the carpentry is in and the dust has settled.
We have a newborn moving in. What should we do first?
Ventilate the nursery daily and air it out before closing it up at night; let new furniture off-gas before the room is occupied; and have the aircon cleaned before the baby moves in so the unit is not holding anything. If the renovation is recent, an air test is worth doing for that room specifically — infants breathe about twice as much air per kilogram of body weight as adults, and sleep long hours in one closed room.
Post-renovation aircon clean?
Chemical wash from $110/unit — clears renovation dust, grime and mould from the coil, blower and drainage. Same-day and island-wide, price confirmed before we start.