Key Takeaways
- Haze rarely damages an aircon. It feels weaker because it has more heat to remove, and the parts that move heat get dirty faster.
- The outdoor unit pulls outdoor air across its fins all day. In haze, fine dust and ash settle on those fins, so it gets rid of heat less well and the air indoors comes out less cold.
- With windows shut and everyone home, the flat holds more heat from people, cooking and devices. One unit is often stretched to cool more space than it was meant for.
- Stale, smoky air feels warmer and stuffier even when the room is at the set temperature. A cheap thermometer settles it.
- Wash the indoor filters yourself. Leave the coil, drain tray and outdoor unit to a Professional. FoamJet aircon servicing starts from $20 per unit.
- For PSI readings and health advice, go to NEA’s official haze site, haze.gov.sg.
Third Hazy Evening, Same Remote, Different Aircon
It’s the third hazy evening in a row in a 4-room flat in Sengkang. The windows have been shut since Sunday, the kids are doing homework in the master bedroom with the door open, and the aircon has been on 24°C since lunch. Everyone agrees it isn’t as cold as last week. Nobody agrees why.
Haze has been back in Singapore since September 2026, and in October the 24-hour PSI reached the Unhealthy range. For today’s readings and health advice, check haze.gov.sg. This guide is about what all that smoke does to your aircon.
What Does Haze Do to Your Aircon?
Not directly. Haze doesn’t change how the refrigerant inside your aircon works. What haze weeks change is everything around it: the parts that move heat get dirty faster, the room has more heat in it, and the air itself feels worse. Each of those makes the aircon seem weaker, and it’s usually a mix of two or three.
| Reason | What’s happening | What to do |
|---|---|---|
| 1. Dusty outdoor unit | Fine dust and ash coat the condenser fins, so heat can’t escape as easily | Leave it to a Professional. Never climb onto the ledge |
| 2. Clogged indoor filter | More fine dust gets indoors, the mesh greys faster and less air passes through | Wash the filters about every 2 weeks while the haze lasts |
| 3. More heat in the flat | Windows shut, everyone home, more cooking and devices on | Draw curtains on sunny windows, keep doors to unused rooms shut |
| 4. One unit cooling too much space | Doors left open so one room’s aircon can cool the corridor or living room | Cool the room you’re in, with the door closed |
| 5. Stuffy, smoky air | Air goes stale with everything shut, and stale air feels warmer | Check the real temperature; air out when readings improve |
| 6. A problem that was already there | Low gas or a dirty coil, noticed now because the unit runs longer | Book a service or a gas check |
Why Does the Outdoor Unit Matter So Much During Haze?
Your aircon is really two machines. The indoor unit picks heat up from the room. Pipes carry that heat out to the outdoor unit on the aircon ledge, where a fan pulls outdoor air across rows of thin metal fins to get rid of it.
That outdoor fan is pulling in hazy air for hours a day. The fins sit very close together, and fine dust and ash settle on them like a thin felt. A coated coil sheds heat less well. When heat can’t leave the outdoor unit, the indoor coil doesn’t get as cold, and the air from your vents comes out cool rather than cold.
Haze in Singapore usually comes between June and October, during the Southwest Monsoon’s warm, dry spells. An outdoor unit on a sun-facing ledge is already working hard in the afternoon, and a dusty coil on top of that is often what tips a room from cold to just about okay.
Don’t try to clean it yourself. Never climb onto the aircon ledge or lean out to reach the unit; that is work at height, for someone with proper safety gear. Don’t hose it from the window either. Water near the electrical parts is a risk, and a hose pushes the dust deeper into the fins rather than out.
Is Your Aircon Filter Clogging Faster in the Haze?
Probably. A split aircon recirculates the air already in your room and doesn’t draw air in from outside. But haze still finds its way in through gaps around windows and doors, and every time the main door opens. If you’re unsure how that works, see what your aircon does during haze.
The filter is a plastic mesh that catches the coarser dust before it reaches the coil. When it clogs, less air moves through the unit, and less air means less cooling, even if the coil behind it is cold.
Check the filters about every 2 weeks while the haze lasts, and once more when it clears:
- Switch the aircon off at the power point.
- Lift the front panel and slide the filters out.
- Rinse them under lukewarm running water. A soft brush helps on the dusty side.
- Let them dry completely in the shade, then slide them back in.
- Don’t run the aircon without the filters. The dust goes straight onto the coil.
Is the Room Just Hotter Than Usual?
Often, yes. In a normal week, the flat empties out during the day and the aircon only runs at night. In a haze week, everyone stays home with the windows shut. People, cooking, laptops, the TV and the afternoon sun all add heat that the aircon now has to remove, for more hours a day.
Many households also open the bedroom door so the cool air reaches the living room. A bedroom unit is sized for the bedroom. Asked to cool the corridor and living room as well, it will run flat out and still feel weak.
- Draw the curtains or blinds on windows that get the afternoon sun.
- Keep the door shut in the room you’re cooling, and shut the doors to rooms you aren’t using.
- Run the kitchen hood while cooking, then switch it off. Exhaust fans push air out, and outdoor air leaks back in through gaps to replace it.
- Leave the remote at 24 to 25°C. Dropping it to 16°C rarely cools the room faster. The unit is already near full power; it just runs longer and uses more electricity.
Why Does the Air Feel Stuffy Even When It’s Cool?
With every window shut, the air goes stale. Breathing, cooking and the smoky smell of haze all build up, and stale air feels warmer and heavier than fresh air at the same temperature. An aircon cools and dries the air. It doesn’t bring in fresh air, and it doesn’t filter out haze.
Put a simple thermometer near where you sit. If the room reads close to what the remote says and still feels stuffy, the cooling is fine and it’s the air you’re noticing. For cleaner air, a portable air purifier is the device built for the job; see air purifier vs aircon during haze. Air the flat out briefly once NEA readings improve.
How Can You Tell If It’s a Real Fault?
Give the unit 15 minutes on cool mode, then hold your hand at the vents. The air should feel clearly cold, not just cool. As a rough guide, air from a working unit comes out about 8 to 12°C colder than the room. If you get much less than that after washing the filters, something else is going on.
These signs point to a fault that a Professional should look at:
- Airflow is still weak after a filter wash.
- Ice or frost on the pipes or the coil behind the filter.
- Water dripping from the indoor unit; see why your aircon is dripping water.
- A hissing or bubbling sound, which can mean low gas; see when an aircon needs a gas top-up.
- The outdoor unit’s fan isn’t spinning, or it is much louder than usual.
- A burning or electrical smell. That isn’t haze. Switch off at the isolator and stop using it.
For the full list of causes outside haze season, read why your aircon is not cooling.
What Can You Do Yourself, and What Needs a Professional?
| You can do it | Leave it to a Professional |
|---|---|
| Wash the indoor filters | Clean the coil behind the filter |
| Wipe the front panel and louvres with a damp cloth | Clear the drain tray and drain pipe |
| Close curtains and doors, set 24 to 25°C | Clean the outdoor unit on the ledge |
| Check the room temperature with a thermometer | Check and top up the gas |
Book a service if the filters are clean and the aircon still feels weak, or if you were already due one. If you can, wait until the haze has cleared so the outdoor unit isn’t coated again straight away. If the unit is struggling now, don’t wait.
Urban Company’s aircon servicing uses FoamJet: foam on the coil fins to lift the dirt, with a fitted cover that drains the dirty water into a bucket. Prices start from $20 per unit. Book aircon servicing in Singapore.
More haze and cooling questions are answered in our aircon servicing guides.
Frequently Asked Questions
Does haze make my aircon less cold?
Not directly. Haze doesn’t change how the aircon makes cold air. It makes the unit work harder: dust and ash coat the outdoor unit so it gets rid of heat less well, the indoor filter clogs faster, and a shut-in flat holds more heat. Together, those make the air from the vents feel less cold.
Does an aircon filter haze?
Not in any meaningful way. The filter in a wall-mounted aircon is a washable plastic mesh that catches visible dust and lint so it doesn’t coat the coil. It isn’t a HEPA filter and isn’t built for the fine particles in haze. During haze it fills up faster, so wash it about every 2 weeks. For cleaner indoor air, use a portable air purifier.
Do I need aircon servicing after the haze?
Not automatically. Wash the filters first. If the aircon still feels weak, smells musty or starts dripping, the dust is likely on the coil, drain tray or outdoor unit, and that needs a Professional. It’s also a good time to book the service you were already due.
Should I service my aircon during the haze or after?
Wash the filters during the haze, about every 2 weeks. For a full service, waiting until the haze clears means the outdoor unit won’t be coated again straight away. If the aircon is struggling to cool now, book it now rather than waiting.
Can I hose down my outdoor aircon unit?
No. The outdoor unit sits on a ledge outside the window, which is work at height, and spraying water near its electrical parts is a risk. A hose also tends to push dust deeper into the fins. Leave the outdoor unit to a Professional.
What temperature should I set the aircon to during haze?
24 to 25°C is sensible. Setting it lower rarely cools the room faster; the unit runs longer and uses more electricity. Keep the door shut and the curtains drawn on sunny windows so the aircon only has one room to cool.
Is it okay to run the aircon all day during haze?
For the aircon, yes. A split unit is built to run for long stretches, and it lets you keep windows shut. It doesn’t clean the air of fine particles, though. For health advice and current PSI readings, follow NEA at haze.gov.sg.
Will an aircon service make my indoor air cleaner during haze?
Not in any meaningful way. A service restores airflow and cooling by cleaning the filters, coil and drain, and it can clear a musty smell. It doesn’t turn the aircon into an air purifier. For cleaner indoor air during haze, use a portable air purifier.