Air conditioner filters, explained

What the filter does

The filter is a screen in the air path of your air conditioner. Room air passes through it before the indoor coil, and it catches dust, lint and pet hair. It keeps grime off the coil and fan, and the air coming back out is cleaner than the air that went in.

Most home air conditioners recirculate the air already inside the house, so every pass through the filter cleans that air a little more. A clean filter matters for the air you breathe as much as for the machine.

On a wall split the filter sits behind the front panel of the indoor unit. On a ducted system it is usually in the return-air grille, the large vent that draws air back to the unit.

The common filter types

There are three kinds you are likely to meet.

• Standard washable filter. A mesh screen that slides out, rinses under the tap and goes back in. It is made to be reused.
• Pleated disposable filter. A folded filter in a frame that catches finer particles than plain mesh. It is not washed. When it is dirty, you replace it.
• Upgraded filtration. Filter grades such as G4, and HEPA-rated options, filter the air more finely again. A dealer fits these and can tell you which your system can take.

Whichever type you have, it still blocks. A finer filter catches more, so it blocks sooner and needs the same routine.

How often to clean or change it

The ACDA e-guide recommends cleaning or replacing the filter every month or two during the cooling season, and more often if the system runs constantly, the house is dusty, or you have pets that shed.

On a ducted system, ACDA's ducted care guide says at least twice a year. Treat that as the minimum. Look at the filter monthly through summer and clean or change it as soon as it looks grey.

A quote from an accredited member must state a recommended servicing frequency. Cleaning the filter is your job between services. The yearly professional service, ideally before summer, covers what a filter cannot protect: the coil and the places where dust, mould and bacteria build up past the filter.

How to wash a filter

The rule in ACDA's bushfire smoke guide is a gentle wash with water, nothing harsher.

1. Switch the system off at the controller.
2. Slide the filter out and note which way round it sat.
3. Take it outside and tap the loose dust into a bin.
4. Rinse it under a tap with plain water. Do not scrub.
5. Let it dry completely before it goes back.
6. Refit it the same way round and switch the system back on.

Pleated disposable filters are made to be replaced, not washed. Note the size on the frame and fit a new one the same size. Your dealer can supply them.

What a blocked filter costs you

A blocked filter chokes the airflow. The fan works harder and the system runs longer to reach the temperature you set. The ACDA e-guide puts a figure on it: cleaning or replacing a dirty, clogged filter with a clean one can lower the air conditioner's energy use by 5 to 15 per cent. It also notes that neglect brings a steady decline in performance while energy use steadily rises.

A blocked filter is also a breeding ground for bacteria, and the dust it can no longer hold ends up on the coil and in the air you breathe. Left long enough, it brings major repairs, or replacement, sooner than necessary.

When to ask a dealer about an upgrade

Ask about better filtration if someone at home has allergies, if you have pets or live on a dusty road, or if bushfire smoke reaches your suburb. The options are a pleated disposable filter, a G4 grade filter, or a HEPA-rated filter. A dealer can fit these to an existing home system.

During bushfire smoke, keep doors and windows closed and run the air conditioner, because it recirculates the air inside the house and cleans it on every pass. If your system has a fresh-air function, turn it off. It draws outside air in, smoke included. For bushfire warnings, follow the NSW Rural Fire Service.

Every accredited member runs a back-up service department, so the business that fits the upgrade can service it afterwards.

If the work falls short

A filter that has got dirty is maintenance, not a dispute. If a member's work on your system falls short, start with the member.

If you cannot resolve it with them, ACDA has a dispute resolution process. Complete the Dispute Resolution Form, attach your quote, invoice and any photographs, and send it to the Dispute Resolution Committee, PO Box 253, Emu Plains NSW 2750, or [email protected]. Where a new domestic installation may fall short of the ACDA Standards, ACDA engages a Chartered Engineer to investigate, report and advise, and arranges for defects to be corrected.

That is the written workmanship guarantee: new domestic installations by an accredited member, contracts up to $25,000 including GST, independent Chartered Engineer review. It is not an equipment warranty and not a price guarantee. A faulty part goes to the manufacturer under its warranty, and your member can help you lodge that claim. It applies in addition to your rights under Australian Consumer Law. ACDA is an industry association, not a regulator.

Your filter routine

• Clean or change it every month or two in the cooling season.
• More often with pets, dust or a system that runs all day.
• Ducted: at least twice a year.
• Wash mesh filters gently with water only and dry them fully.
• Replace pleated disposable filters rather than washing them.
• Turn off the fresh-air function when bushfire smoke is about.
• Book a professional service once a year.

Every accredited member runs a back-up service department, so the same business can service your system and fit a filter upgrade. Find one near you.