Every time the PSI starts climbing, our WhatsApp fills up with the same two questions. Should I switch off my aircon so it does not suck in the haze? And can I buy some special filter that cleans the air? One of these fears is a myth, and one of these hopes is half true. Let us go through both properly, because during haze season bad information spreads faster than the smoke.
First, the myth: your aircon does not pull in outside air
This surprises a lot of people. The split type aircon in your HDB flat or condo does not bring fresh air in from outside. The indoor unit recirculates the air already inside your room, cools it, and blows it back out. The outdoor unit on the ledge is only there to dump heat. The two units exchange refrigerant through the pipes, not air.
We wrote a full explainer on this in our post on whether an aircon can bring in smoke, but the short version is simple. If your windows and doors are closed, running the aircon does not import haze. The haze that gets into your home comes through open windows, door gaps and ventilation openings, not through the aircon.
So should you run the aircon during haze?
Yes, and for most homes it is actually the sensible move. Here is why.
When the haze is bad, the official advice is to stay indoors and keep windows closed. In Singapore’s climate, a closed up flat turns into an oven by mid morning. The aircon is what makes the closed window strategy livable. You keep the smoke out and stay comfortable at the same time.
Running the aircon also dries the air slightly, which most people find more comfortable when everything outside smells of burning. And because the air keeps moving through the indoor unit, the filters catch some of the larger particles that drifted in before you shut the windows.
Now the honest part: what your aircon filter can and cannot do
This is where we have to be straight with you, because plenty of sellers are not.
The standard mesh filter in your aircon is a dust screen. Its job is to protect the coil inside the unit, not your lungs. It catches hair, lint and larger dust. The fine particles that make haze dangerous, the PM2.5 stuff, sail straight through it.
Anti bacterial and enhanced filters help at the margins, and we covered them honestly in our post on anti bacterial aircon filters. They are better than the bare mesh. They are not even close to a HEPA filter, and any aircon salesman telling you a wall mounted split will scrub PM2.5 from your air is selling you a story.
If someone in your home is elderly, very young, pregnant or asthmatic, the combination that actually works during haze is this. Aircon running with windows closed to keep the home sealed and cool, plus a standalone air purifier with a true HEPA filter for the fine particles. We install aircons for a living and we do not sell purifiers, so take that as an honest recommendation rather than a pitch.
What haze does to your aircon
Haze is not just bad for people. Weeks of fine particles hanging in your indoor air means your aircon filters and coil load up noticeably faster than usual. We see it every haze season. Units come out of a bad haze period with grey, matted filters and a fine coating on the coil that regular monthly cleaning would normally take months to build up.
Two practical habits during a haze period:
Wash your filters every one to two weeks instead of monthly. It takes five minutes under the tap. A loaded filter chokes airflow, makes the unit work harder and pushes up your bill exactly when you are running the aircon the most.
Book a proper service once the haze clears. The fine particles that got past the mesh end up on the coil and blower wheel where home cleaning cannot reach. A normal servicing after the season resets the unit. If the smell of smoke lingers when the aircon runs, that is the coil and blower telling you they need attention.
A simple haze day routine
When the readings climb, this is the routine we give our own customers. Close the windows early in the morning before the air indoors gets smoky, not after. Run the aircon on your normal settings, there is no special haze mode needed. Wipe down or wash the aircon filters weekly. Run a HEPA purifier in the bedroom if you have one, sized for the room. Check the official NEA readings rather than judging by smell, and follow the health advisories for outdoor activity. Then book a servicing when the skies clear.
That is it. No panic, no gadgets you do not need.
The one situation where haze and aircon do mix badly
If your home uses a fresh air intake, which is rare in HDB flats but appears in some condos, landed homes and offices with ducted systems, then outdoor air genuinely is being drawn in. Those systems have their own filters that need checking during haze, and some can be switched to full recirculation. If you are not sure what your setup does, send us a photo on WhatsApp and we will tell you what you are looking at.
After the haze
The units that suffer most are the ones that went into haze season already dirty. If your aircon has not been serviced this year, doing it before the next haze period means cleaner filters, a cleaner coil and better airflow exactly when you need the unit working at its best. With seven teams across the island we can usually schedule a servicing within a day or two.
Questions about your specific unit or a smoky smell that will not go away? WhatsApp us at +65 8818 5781 and we will give you a straight answer.
