Need to know
- Air conditioner dust filters aren't designed to remove smoke or germs, but some models have air purification filters, which can help
- Most of the air conditioners we've recommended have some form of air purification filter
- A dedicated air purifier with a HEPA filter is a better bet for cleaning indoor air of smoke, viruses and other pollution
With air purifiers selling out in many stores around Australia following concerns about the COVID-19 virus, bushfire smoke and just general indoor air quality, we've been asked a new question about air conditioners lately: can an air conditioner filter out viruses, bushfire smoke or other pollution once it's inside your home?
Unfortunately, most air conditioners aren't built for that type of air filtration.
But there are some types of air conditioner filter that could prove useful in helping keep the indoor air clean.
In-built dust filters won't do much for smoke
All air conditioners have a dust filter in the indoor unit. This traps dust from the air as it circulates through, mainly to stop it clogging up the internal workings.
But a dust filter will only have a minimal effect, if any, on smoke and other fine particles.
Check the instructions for how to access the filters and how often you should clean them. Clean filters allow easier airflow and help your air conditioner run more smoothly and efficiently.
Ionisation filters can help with smoke – a bit
Some air conditioners include an air purification filter based on ionisation. There are a few variations on this type, including photocatalytic and plasma stream filters.
Ionisation filters can remove at least some smoke, but usually the claims for these filters focus on the removal of fine dust, mould spores, odours, allergens and germs.
How does an ionisation filter work?
Ions (charged particles) are generated inside the air conditioner's indoor unit, and are used to trap or break down pollutant particles such as dust, pollen or bacteria.
The ions may be spread through the room, or they can be generated on the surface of a catalytic plate inside the unit.
The ions attach to the pollutant particles, and then the particles either:
- break down through oxidisation
- become negatively charged and then trapped on a positively charged plate inside the unit
- precipitate out of the air and cling onto the floor or other surfaces, where they can be vacuumed or wiped away.
Are ionisation filters common in air conditioners?
Many major brands offer some form of ionisation-based air purification filter, usually in their most recent or premium model ranges.
- Daikin (flash streamer, or plasma stream)
- Fujitsu (ion and catechin)
- Hitachi (Nano Titanium Wasabi)
- Kelvinator (Bio-HEPA and ion)
- LG (Plasmaster Ioniser)
- Mitsubishi Electric (PlasmaDuo)
- Mitsubishi Heavy Industries (photocatalytic and allergen filters)
- Panasonic (nanoe-G and nanoe-X).
Any downside to using these filters?
They'll need cleaning and replacement from time to time. Check the unit's instructions.
And ionisation can create small amounts of ozone, which can be an irritant to breathing. It's hard to say how significant the amount of ozone would be, but it's a factor to consider if you suffer from asthma or any other respiratory disorders.
Some models also offer a catechin-based filter. Catechin is a plant extract with antifungal and antibacterial properties. Catechin filters are intended to trap and eliminate bacteria, mould spores and some other fine particles.
The risk of buying an aftermarket air purifying filter
A quick look online shows various aftermarket air purifying filters for air conditioners, described as electrostatic, activated carbon or similar. They claim to be compatible with major air conditioner brands and in some cases can be cut to size to suit different models.
Be cautious with any such filters. While they may provide filtration as claimed, it's highly unlikely that they've been thoroughly tested with every air conditioner brand, and using non-genuine parts may reduce your air conditioner's performance, possibly cause damage and could void your warranty.
HEPA filters are still the best option
The best way to filter out very fine particles such as smoke, mould spores, pollen and viruses is with a HEPA filter (high-efficiency particulate air), which are in many vacuum cleaners and most air purifier units, but not in air conditioners.
Generally, HEPA filters only work well at low airflow levels, due to the density of the filter. That means they can't practically be fitted to domestic split-system or ducted air conditioners, which often have to deliver much greater volumes of airflow than a dedicated air purifier.
It's possible, with extensive redesign, that domestic air conditioners with true HEPA filtration might appear in the future.
Kelvinator's current range of split-system models have "Bio-HEPA" filters, along with an ion filter.
We haven't seen the technical details, but a Kelvinator spokesperson advised that if you're looking for a meaningful amount of purification, you should be looking at air purifiers rather than split-system air conditioners.
This suggests that the effect of these Bio-HEPA filters is limited. Given how they're fitted, it seems likely that only some air ends up passing through the air purification filter while the rest flows around it.