How to choose an air purifier: 3 important things to know

Air purifier Dyson Big Quiet
Image: Dyson.

With hay fever and bushfire season upon us, choosing the right air purifier ensures your household will breathe easy this summer.

There was a time when if you were in need of some fresh air you could simply crack a window, but these days it’s just as likely that the air outside is the problem. Australia’s bushfire season is getting longer, with a higher frequency of dangerous fire weather days which can see residential areas blanketed in smoke even if they are far from the flames.

It’s a significant issue, considering that 2.7 million Australians are affected by asthma and around 7 million more are at elevated risk of developing health problems during extreme smoke events. Over one week during the Black Summer bushfires of January 2020, there was a 44 per cent increase in patients reporting asthma symptoms and presenting to emergency departments, according to the Australian Institute of Health and Welfare

Filter out the nasties

Choosing the right air purifier for your home depends on exactly why you need one, the size of the room in which you’ll use it and when you’ll put it to work.

There are many different ways to monitor air quality, but the main pollutant emitted by bushfire smoke is fine particles with a diameter of 2.5 microns or less (also known as PM2.5). These are small enough that they can get deep into the lungs and even find their way into the bloodstream. Meanwhile, common larger PM10 sources include smoke, dust, pollen and mould.

Portable air purifiers fitted with high-efficiency particulate air (HEPA) filters can substantially improve indoor air quality during bushfires, according to CSIRO.

They come in different grades, with H13 HEPA filters trapping at least 99.95 per cent of dust, smoke, mould and other airborne particles. Grade H14 increases this to 99.995 per cent.

Air purifiers can also contain a range of other filters. Carbon or charcoal filters can trap odours and Volatile Organic Compounds (VOCs) such as formaldehyde, which can irritate the eyes, nose and throat, as well as cause difficulty breathing. 

Ozone filters are also good for removing odours but not effective at removing air pollution. By producing ozone, they can cause breathing irritation. Meanwhile, ionic or ionisation filters are good for removing fine particles such as dust and smoke, but ionisation of air can produce ozone.

Clear the room

Choosing the right air purifier also requires ensuring that it is large enough for the room.

The Clean Air Delivery Rate (CADR) is an industry standard for measuring the volume of air that the air purifier can clean – expressed in cubic metres per hour, or sometimes cubic feet per second. The larger the room, the higher the CADR required.

As a rule of thumb, look for a CADR rating 12 times the floor area of the room you’re trying to purify, assuming a standard ceiling height of 2.4 metres. So in a 3 x 3 metre room, look for a CADR of at least 108 (3 x 3 metres equals 9 square metres of floor area, times 12 equals 108).

Keep it quiet

Also consider how noisy the air purifier will be and whether it will just run in the living area during the day or also in the bedroom at night.

Noise levels are measured in decibels (dB) – a whisper is around 30 decibels, while normal conversation is about 60 dB. A hairdryer cranks it up to 70 dB, while a vacuum cleaner pushes 80 dB.

Each air purifier operates at different noise levels depending on its fan level, so look for a variety of speeds, including an extra-quiet nighttime mode.

Ignore claims of “whisper quiet operation”: an air purifier’s actual noise levels should be listed in the product specifications. If it’s going to run by your bedside, look for a mode that operates at 40 dB or less.

More on air purifiers at GadgetGuy.