Should you run the aircon during haze?

Running the aircon during haze

You can keep the aircon running through a haze episode. It cools the room, but its standard filter is not designed to remove fine haze particles. The aim is to keep hazy outdoor air out of the flat and let the unit cool the indoor air it recirculates.

The National Environment Agency (NEA) gives practical tips for households in its haze FAQ. Close doors and windows when the outdoor air quality appears to be worsening. Fans or air-conditioners may be used for air circulation and cooling. If an air-conditioner draws in unfiltered air from outside, as window units can, close its outdoor air intake opening. NEA also suggests cutting down other indoor sources such as cigarettes and candles, and re-opening windows and doors when air quality improves.

During haze, NEA publishes a 24-hour Pollutant Standards Index (PSI) forecast range with a health advisory. Checking it each day helps you decide when to keep the flat closed and when it is reasonable to open up again.

A typical wall-mounted split unit recirculates the air already in the room rather than pulling air in from outside. Models differ, so check the manual for your unit to see how it handles outside air before you rely on it during haze.

Aircon filters and air cleaning devices

The filter behind the front panel of a split aircon catches dust. Think of it as a dust filter rather than a haze aircon filter: it is not designed to remove the fine particles that make up haze. It also needs to stay clean, because a dirty filter restricts airflow.

For fine particles, NEA's haze FAQ says portable air purifiers can be used to further reduce the indoor particle level, and that highly efficient filters such as HEPA filters are preferred. Choose a purifier sized for the room you will use it in.

NEA's air cleaning devices page describes portable air cleaners as compact stand-alone appliances designed to keep particle levels low in an enclosed space. It explains the Clean Air Delivery Rate (CADR), which is the amount of clean air a device can produce for a room. A higher CADR means a greater ability to return clean air. Knowing the CADR and your room size helps you make an informed purchase, so ask suppliers for detailed product information before you buy.

A separate guide looks at the air purifier vs aircon question in more depth. If you are still deciding which type of unit suits a room, see how a portable, window or split aircon compares.

Fresh air when the haze lifts

When the readings improve, let fresh air back into the flat. NEA's ventilation guidance says occupants of residential homes may improve ventilation by opening doors and windows, and that fans can be used to promote air circulation when needed.

In practice, open the windows and doors you kept shut, and run a fan for a while to help move the stale air out. If the haze comes back, close up again.

Airing out is also a good time to deal with dust that settled during the haze. NEA's haze FAQ suggests wet-cleaning settled dust by mopping or wiping rather than dry-dusting.

Clean the filter afterwards

NEA's energy saving tips say to check the aircon filter once a month and clean or replace it when necessary. After a haze spell, check it sooner rather than waiting for the monthly check, especially if the unit ran for long hours with the windows shut.

Look for a layer of dust on the filter mesh. A dirty filter restricts airflow, so a weaker breeze than usual is another sign it needs attention.

For the steps to remove, rinse and dry the filters, see the guide on how to clean an aircon filter.

If the unit gives off a stale or damp smell when you go back to normal use, see what to check when your aircon smells musty.

Running costs and servicing

Running the aircon for longer hours with the windows shut raises your electricity bill. NEA's energy saving tips suggest setting the temperature at 25 degrees C and servicing aircon units regularly. For more ways to keep the bill in check, see the guide to aircon settings to save electricity.

A haze spell is also a sensible point to think about servicing. If the filter is clean but airflow stays weak, or the unit is due for its regular service, book aircon servicing. The cost depends on the job, the number of units and the type of service, so compare what companies publish and ask what each visit includes before you choose.

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