Air purifier buying guide

When you need an air purifier

Anything you breathe in, other than air and water vapour, is a pollutant. This includes dust, pollen, smoke, volatile organic compounds (VOCs), pet hair and dander.

If you have allergy sufferers or asthmatics in the house, an air purifier can help to alleviate some of their symptoms. Air purifiers work by sucking the air in the room into the unit and across a filter to remove particles from the air. That way, you breathe filtered, clean air that doesn’t trigger reactions.

Air purifiers can also be handy if you live in built-up areas with high pollution (including wood smoke) that you don’t want to breathe in.

Viruses and bacteria

An air purifier fitted with a HEPA filter can remove airborne bacteria and viruses. While viruses like the Covid-19 virus are smaller than the miniature holes in a HEPA filter (0.1 microns while a HEPA filter is 0.3 microns), they go where the wind blows them and they can still easily get trapped against the fibres and get removed from the air.

While that may help, it doesn’t completely eliminate the danger posed by bacteria and viruses – it doesn’t help with contaminants sitting on a surface. You need to wipe down surfaces, practice good hygiene and wear a face mask to maximise your protection.

What to consider when buying an air purifier

A good filter is the most important part of an air purifier, though that doesn’t always guarantee excellent performance. However, there are additional considerations when buying an air purifier.

Room size 

Manufacturers of air purifiers usually state the maximum recommended room size in metres squared (m²). Choose an air purifier that can handle a larger area than the room you'll usually use it in. That way, it won't have to work as hard to clean the air, so it should run more quietly too.

HEPA filters 

HEPA filters are the mainstay in air purifiers, so make sure your chosen model has one. They can trap particles down to 0.3 microns, which should deal with most airborne nasties. For reference, a human hair is about 80 microns.

Ionisation filters 

An ioniser works by using a high voltage to put a charge through airborne particles to make them static. This makes them attracted to grounded objects, which removes them from the air.

Charcoal  filters

Charcoal filters remove odours and they can help absorb VOCs.

Pre-filter s

Pre-filters are a layer of defence in front of the purifying filters. Pre-filters catch larger bits of debris to stop the finer filters from getting clogged up too quickly.

Sensors and timers 

An air purifier with a built-in pollution sensor will continuously check the air quality. Some models will switch on once they detect contaminants. In the absence of automatic sensors, an air purifier will chug away non-stop, so look for a model with a timer so you can set the unit to run at certain times of the day.

Fan  speeds

A good range of fan speeds is important for quickly clearing all parts of the room, as well as having some quieter settings for when you go to bed.

Heating function

Some air purifiers can also heat (and sometimes cool) your home. Check our air purifiers reviews to see which models have a heating function.

Filter replacement

Air purifier filters have a limited lifespan as they the airborne pollutants they trap clog them up over time. Check the expected lifespan of the filter of any air purifier you're considering buying as some last as little as 6 months.

Also make sure replacement filters are readily available and check what they cost.

Air purifier features to ignore 

Ozone air treatment: This is sometimes called ozone generation. It's just marketing hype. Many studies have shown it to be ineffective at treating airborne contaminants.

UV sterilisation: Manufacturers claim some of their air purifiers use UV light to kill bacteria. While UV light is proven to sterilise water, studies have shown that domestic air purifiers claimed aren't effective at sterilising airborne bacteria with UV light.