How to Look After Your Air Conditioning Filters

Why filters matter

The filters fitted inside an indoor air conditioning unit exist to catch dust, hair, fibres and other airborne particles before the air passes over the coil. Without them, the coil would quickly become clogged with debris, reducing airflow and efficiency and making the unit work harder than it needs to.

A clean filter isn't just about air quality, it directly affects how well the system cools or heats a room and how much electricity it uses to do so.

How often to clean them

For most households, cleaning the filters every four to six weeks during periods of regular use is a sensible starting point, more often in dusty environments, homes with pets, or rooms that see heavy use. In a commercial setting with higher footfall, monthly checks are worth building into a routine.

If you've never checked your filters and the system has been running for months, it's worth doing this straight away rather than waiting for a scheduled reminder.

How to clean a filter

• Switch off the unit at the isolator or wall control before opening the front panel
• Lift the front cover and slide the filters out, they usually clip or slide free without tools
• Vacuum off loose dust first to avoid pushing debris deeper into the mesh
• Rinse gently under lukewarm running water, front to back, using a soft brush for stubborn dirt
• Shake off excess water and leave to air dry fully before refitting, never refit a damp filter

Signs your filters need attention

A visible layer of grey dust or discolouration across the mesh is the clearest sign. You might also notice reduced airflow from the unit, a musty smell when it starts up, or the system seeming to run longer than usual to reach the set temperature.

Some units have an indicator light or icon on the remote that reminds you to clean the filter after a set number of running hours, which is a useful prompt if you tend to forget.

What filters can't fix

Filter cleaning is maintenance you can do yourself, but it isn't a substitute for a full service. Internal coil cleaning, refrigerant checks, drainage checks and electrical inspections need to be carried out by a qualified engineer, ideally once a year for domestic systems and more frequently for commercial installations.

Replacing rather than cleaning

Standard mesh filters can usually be cleaned and reused indefinitely, but some systems use additional filtration layers, such as odour or fine particle filters, that are designed to be replaced rather than washed. Check your unit's handbook, as washing a filter that's meant to be replaced can damage it and reduce its effectiveness.