Air purifiers

An air purifier draws room air through a filter and blows it back out. How much it cleans depends on its clean air delivery rate (CADR) against the size of your room, not on the brand. After that, the differences you live with are noise on the lowest setting, the filter class and what replacement filters cost each year.

Slim grey air cleaner beside a made bed in a lamp-lit bedroom at night

Before you buy

  • Match the CADR to the room. Measure the floor area in m² and look for a CADR in m³/h of about 12 times that figure, which gives roughly five air changes an hour. Brand room-size claims often assume fewer. Our guide to what size air purifier you need shows the maths.
  • Price the filters as well as the purifier. Every main filter has a part number and a change interval. A cheap purifier with dear filters changed twice a year can cost more over a few years than a pricier one. Our filter finder lists every model’s part number and interval.
  • Check the noise on the setting you will use. For a bedroom, the lowest-setting figure and whether the lights switch off matter more than top-speed noise, which you only hear during a quick clean.

Top picks

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Every air purifier we track

More air purifiers

Showing 10 of 10 air purifiers

We compared each purifier’s published clean air delivery rate, noise on the lowest setting, filter class and filter interval, checked prices at UK retailers and read owner reviews where we could. We don’t lab-test purifiers, and where a maker publishes no CADR we say so. How we choose.

Air purifiers questions

What size air purifier do I need?

Measure the floor area. In a room with a 2.4 m ceiling, about five air changes an hour needs a CADR in m³/h of roughly 12 times the area in m², so a 15 m² bedroom wants around 180 m³/h. Brand room-size claims often assume fewer air changes, so compare CADR.

How often do I need to change the filter?

It depends on the model and how many hours a day it runs. Each product page gives the maker’s interval for the main filter and its part number. On most models the filter light counts running time rather than testing the filter, so change it when the light comes on, even if the filter still looks clean.

Are compatible filters as good as genuine ones?

Levoit says non-genuine filters can throw out its filter-life reminder, and Coway and Meaco exclude damage from parts they haven’t approved from their warranties. A compatible filter may fit, but the purifier’s maker hasn’t checked its grade. Match the part number before you buy.

Will an air purifier help with hay fever?

The NHS hay fever advice is to keep windows and doors shut where possible, vacuum often and dust with a damp cloth; it says nothing about purifiers. Allergy UK suggests purifiers for year-round allergies to indoor triggers such as dust mites. A purifier is not a treatment: ask a pharmacist or GP about symptoms.

Are ionisers safe?

UK government advisers (SAGE-EMG, 2020) did not recommend ionisers and other non-filter add-ons unless shown to be safe, because they can create irritant by-products such as ozone. Each product page says whether a model has an ioniser and whether it switches off.

Does an air purifier replace opening the windows?

No. It filters the air already in the room and adds no fresh air, and UK government advisers say it should never be a reason to ventilate less. Keep extractor fans and trickle vents working.

Want it to do more than purify? Compare purifier fans and heaters, which cool you or warm the room as well, and purifier dehumidifiers and humidifiers for damp or dry rooms.

Image credits: Home Air Quality Guides (homeairguides.com), CC BY-SA 2.0