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How to buy the best air purifier

By Matt Stevens

Expert tips on how to buy the best air purifier that will clean the air in your home quickly and effectively and without making too much noise.

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Want to buy the best air purifier? Then choose carefully. A good-quality air purifier will do a great job of cleaning the air in your home. The most helpful purifiers will do this automatically when they sense a dip in air quality.

But there are plenty of air purifiers on sale that aren’t powerful enough to clean air quickly enough. Our tests uncovered one model that’s so underpowered and ineffective that we’ve made it a Don't Buy air purifier.

As it’s important to buy an air purifier that does a good job of cleaning air quickly, we think it’s worth doing some research before heading to the high street, or online, to buy a new machine.

Our video (above) shows how to buy the best air purifier, how much you should spend to get a good one and what to look for in the shops.

In our tough lab tests we uncover the air purifers that remove the most polluting particles from the air, are quiet and easy to use. Take a look at our recommendations for the best air purifiers.

Who needs an air purifier?

If you suffer from allergies, an air purifier would be a good investment. Provided you buy the right model.

Our tests show that using an air purifier in your home will reduce the number of pollutants in the air, such as dust, pollen and smoke. All of the models we’ve tested removed at least some particles from the air, but the difference between the best and worst is enormous.

The best air purifier for removing dust was more than 26 times more effective than the worst.

In our lab tests, we found that the best air purifier for removing dust was more than 26 times more effective than the worst. In your home, this means it would take much, much longer to clean the air, which is no good for you if you’re allergic to household dust.

Are fast air purifiers better than slower ones?

In the same way that it’s more helpful if a heater can heat your home more quickly, we think it’s better for an air purifier to clean air quickly. That’s why we award higher test scores to those air purifiers that quickly removed the particles used in our tests – pollen, dust and smoke particles – more quickly.

How much do air purifiers cost?

You can buy air purifiers for little more than £100 and prices go right up to more than £600. But to be confident you're buying an air purifier that does a good job of cleaning the air effectively, you’re likely to need to spend at least £200. But spending this much doesn’t guarantee you’ll end up with a great machine - we’ve tested models costing £450 that are less effective than purifiers that are £200 cheaper.

We’ve tested machines costing £450 that are less effective than purifiers that are £200 cheaper.

How much do air purifiers cost to run?

We work out how much each air purifier we tested would cost to run, based on being used for 12 hours a day. 

  • £72 per year - approximately how much the most powerful air purifiers are likely to cost
  • £40 a year - what medium-sized machines are likely to set you back  
  • £26 a year - how much a smaller air purifier is likely to cost you.

The smallest and least powerful air purifier we tested cost just £3 a year to run.

To find out more about how much each air purifier we’ve tested will cost to run,  check out our air purifier reviews. 

Types of air purifier

Desk air purifiers

As the name suggests, desk air purifiers are compact enough to sit on a desk or a shelf in your home. They’re not as powerful as bigger machines, but tend to cost less to run and can be effective in small rooms. 

But read our air purifier reviews before you buy, as one desk air purifier we tested didn’t pack much of a punch at all – it was 26 times less effective at extracting dust from the air than the best we tested.

Tower air purifiers

Tower air purifiers are tall and often cylindrical. They can be powerful enough to work in large open-plan spaces in the home. In terms of dimensions, some can be as large as a tall, cylindrical kitchen bin. Others are roughly the same height but much slimmer.

Large portable air purifiers

This type of air purifier is roughly the size of a hand luggage flight case and the best are able to effectively clean the air in a large living space. 

Some can be the most powerful in terms of wattage, which pushes up running costs. But most are mid-range, power-wise.

Oscillating air purifiers

Oscillating air purifiers can be fan or desk based machines and can be set to move round as they clean the air.

Air purifiers that double as fans

The Dyson Pure Cool Link TP02 (£450) tower air purifier and the Dyson Pure Cool Link DP01 (£350) desk air purifier both come from Dyson’s air cooling, heating and cleaning range and sport the recognisable appliance-with-a-hole-in-it design.

Hepa filters

Air purifiers use an array of filters to capture pollutants. These are often made up of a large particle filter, which can be re-used and washed, as well as other finer filters - usually including a disposable Hepa filter. The Hepa filter’s lifetime is limited by how often you use your machine.

Manufacturers often advise that Hepa filters should be replaced every six months to keep air purifiers working efficiently. But if you only use an air purifier every now and then, rather than every day, your filters will last much longer without becoming clogged with particles. Good machines include a filter-replacement indicator, which shows when the Hepa filter is full and ready to be replaced.

New Hepa filters can vary in cost, depending on which air purifier you buy. Replacement Hepa filters for the Vax ACAMV101 and the two Dyson air purifiers we’ve tested are £50. Filters for the Philips AC3256/30 cost £30. DeLonghi AC150 filters are cheapest at £20.

How to make air purifier Hepa filters last longer

One way to save money is to clean the Hepa filters yourself. Which? member Brian from Watford told us: ‘A gentle vacuum once a month keeps them going for up to a year.’

Do this outside to avoid re-introducing captured allergens to your home. And be careful how you use your vacuum cleaner – air purifier filters are delicate and can become damaged by vigorous vacuuming.

Noise generated by air purifiers

One in ten owners* we spoke to told us their air purifier affected their sleep. This is why we test the noise produced by models on their highest and lowest power settings, so you’ll know which air purifiers are the least likely to disturb you.

The difference between lowest and highest settings can be the difference between hardly being able to hear the air purifier and an annoying and rumbling whine. For four of the ten air purifiers we’ve tested, the lowest setting was noticeably quieter.

The quietest machines do a very good job of keeping noise to an absolute minimum, both on the lowest and highest setting.  We’ve tested some that you can hear when on full power, but we wouldn’t say the noise was intrusive.

*We surveyed 1,337 Which? members in January 2017 and asked them about their experiences of using an air purifier. 

Unless you can try out an air purifier before you buy, the only way you can tell if it's likely to disturb you or not is to read our air purifier reviews.

Automatic mode and air sensors

Air purifiers with air sensors sniff out pollutants. They can be set to switch themselves on and set their power levels according to the air quality. 

So if you live beside a busy road and traffic starts to build up, an air purifier with a built-in air sensor will spring to life and start cleaning the air. This can also prove handy in summer if you have hayfever.

Do you suffer from a pollen or dust allergy? Find out which models remove the most pollen and dust from the air – see our air purifier reviews.

Air purifier timers

Air purifiers with timers can be set to switch on and turn off. This is helpful if the purifier doesn’t comes with an air sensor, as it means you can set it to switch on and start cleaning the air before you get home.

Night mode and air purifiers

Night mode should mean quiet air purification, sometimes with dimmed lights, to help you sleep. But our tests show that night mode isn’t always quieter than the lowest speed setting. So if you can’t sleep with your air purifier set to night mode, try turning the power down a little to see if it makes it any quieter.

Smart air purifiers

Smart air purifiers can be set from your phone. Easy-to-install apps allow you to link to the purifier. As well as being used to set the machine, the apps also show the air quality in your home.

The Dyson Pure Cool Link TP02 (£450) and the Dyson Pure Cool Link DP01 (£350) and the Blueair 480i (£629) are all smart purifiers. 

Go to our air purifier reviews to find out which apps and smart functionality we liked best.


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