Aircon during the haze season: what it can and can't do

A split aircon cools the air already in your room; it does not pull air in from outside. That is the first thing worth knowing during a haze, because it means a closed-up unit is not drawing the haze indoors the way an open window would. Run with the windows shut, it keeps recirculating the same indoor air.

What it does not do is clean that air of haze. The fine particles that make haze a health concern pass straight through a standard aircon filter, which was built to catch dust, not smoke. Running the unit harder cools the room faster but does nothing to the particles hanging in it.

So the aircon's real job in a haze is comfort and sealing, not filtration. It keeps the room cool enough that you can stay shut up against the outside air. Clearing the fine particles is a separate job, and it needs a separate machine.

The filter in a wall unit is a coarse mesh. It traps hair, lint, and the larger dust that would otherwise foul the coil, and it does that job well. Haze particles are far smaller, and they slip through the same mesh as if it were not there.

This is why an aircon and an air purifier are not interchangeable. The aircon keeps the room cool and sealed; a purifier with a HEPA filter is what actually removes the fine particles. Expecting one machine to do both jobs is the common haze-season mistake.

Keep windows and doors shut and let the aircon hold the room cool. A sealed room with the unit recirculating is the cleanest air you will manage at home during a bad spell, because you are not letting fresh haze in to replace what settles. Opening up to air the room undoes it.

Pair it with a HEPA purifier sized for the room to handle the particles the aircon cannot touch. The two work together: the aircon manages temperature and keeps the room sealed, and the purifier manages the fine particles. Neither replaces the other.

Clean the filter more often than usual while the haze lasts. A spell of haze loads a filter far faster than ordinary weeks, and a clogged filter weakens both airflow and cooling just when you need the room to stay shut and comfortable.

A prolonged haze leaves its mark inside the unit. The same fine dust that hangs in the air settles on the filter and the coil, loading them faster than a normal month would. A filter that was clean before a haze week can come out visibly grey after it.

The signs are the usual ones, arriving sooner: airflow that feels weaker, a faint dusty smell when the unit starts, and cooling that lags. Treat them as the unit asking for a clean, not as a fault. Left through a long spell, a caked coil can drift from a simple filter clean into needing a chemical service.

When the air clears, give the unit the attention the haze earned it. Clean or replace the filters first, since they carry the most of what the unit pulled in. If cooling still lags or a dusty smell lingers after a filter clean, the coil has likely taken on more than a rinse will shift, and a chemical service is the next step.

A unit that came through a heavy haze running hard is worth a proper look, not an assumption that it bounced back. If the airflow or the smell has not returned to normal, describe what changed and have it assessed. Better that than letting the next hot stretch load it again.