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30 July 2021

How to buy the best air purifier

The best air purifiers clean the air in your home quickly and effectively, and without making too much noise. Use our expert advice to make sure you buy one of the best air purifiers
Christina Woodger
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The best air purifiers will do a great job of cleaning the air in your home. But there are also plenty of air purifiers that struggle to tackle common household allergens – including some expensive models.  

'Air purifier' is a popular term for these machines, so that's how we refer to them, but 'air cleaner' is more accurate. These machines don't leave you with sterile or completely pure air, but they can make your air cleaner. 

The best air purifiers will improve the air quality in your home quickly without making too much noise or using too much energy. The worst will be significantly slower, trapping far fewer particles in the same time period, and potentially making more noise and using more energy in the process. 

Some air purifiers are great all-rounders, while others are better at tackling one type of pollutant than another. If you've got hay fever, for example, your priority might be picking an air purifier that's great at trapping pollen.

Not sure which type of air purifier to buy? Scroll down to find out if an air purifier is right for you, the types available, and how much you should expect to pay. 

Best air purifiers

We've put the most popular air purifiers on the market through our tough lab tests. Log in or join Which? to reveal our Best Buys in the table below.

  • 85%

    This air purifier does a great job of clearing pollen particles from the air. So, if hay fever routinely ruins your summer, it could really help you. It’s our third best air purifier for trapping pollen, and our joint-top air model overall. It’s also fairly cheap as far as air purifiers go.

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  • 85%

    This air purifier removed dust, pollen and smoke from the air swiftly in our tests. It's also energy-efficient, quiet on its low fan speed, is generally easy to use and comes with plenty of extra features

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  • 84%

    This air purifier did a terrific job of removing dust, pollen and smoke from the air in our tests. It has an LED digital display, a timer, a night mode, an automatic mode and three fan speeds. It’s also controllable via wi-fi from a smartphone app. It is expensive, though.

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Tables last updated July 2021. 

Still haven't found the perfect model for you? See all of our air purifier reviews

We can't specifically test with traffic pollution particles: we test with dust, pollen and smoke particles, as these are common household allergens. However, an air purifier that performs well in our dust tests is likely to also do a good job of trapping harmful PM2.5 particles found in traffic pollution, which are of a similar size to dust: 2.5 microns (µm). 

Particles are only one aspect of traffic pollution, though: gases such as NO2 (nitrogen dioxide) are also an issue, and cannot be filtered due to being too small. If you can, buy an air purifier with a carbon filter, as carbon filters are designed to trap gases. 

Video: how to buy the best air purifier

Watch this video to help you buy the best air purifier for you.

Do I need an air purifier?

An air purifier shouldn't be your first line of defence against air pollution. 

The best way to control indoor air pollution is to eliminate the source of the pollution and to ventilate. Minimise your use of products that cause indoor air pollution, such as chemical sprays. Keep humidity under control, so that biological contaminants don't thrive, and employ good hygiene practices. And open windows, particularly when you've just carried out an activity that causes pollution. 

Before resorting to an air purifier, consider ways to improve ventilation in your home, and check our guide on improving indoor air quality

If it's not possible to increase ventilation – your outdoor air quality is poor, say, or you suffer from hay fever and can't leave windows open for long periods in case pollen comes in – then an air purifier could be a good investment, provided you buy the right model. Remember that you'll need to close the doors and windows to the room with the air purifier, so that you're not letting in more pollution for it to tackle. 

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 particles. 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.

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 or pollen. 

Here's our full list of Best Buy air purifiers.

Best air purifiers: woman with allergies

What features should I look for on an air purifier? 

HEPA filter

A HEPA (high-efficiency particulate air) filter is a type of air filter that uses a combination of trapping mechanisms. 

EU standards state that to use the term HEPA a filter must remove at least 99.95% of tiny particles with a diameter of 0.3 μm (micron). 

Keep an eye out for filters with marketing names such as HEPA-type, HEPA-style and so forth, as there's no guarantee that they will conform to the same criteria. 

An air purifier with a HEPA filter is more likely to do a good job than those with another type of filter. We’ve reviewed most of the air purifiers on the market, but if you’re buying one that we haven’t reviewed, buy one with a HEPA filter. 

A HEPA filter doesn’t guarantee that an air purifier will be good, though, as there are other aspects to an air purifier that might make it a bad machine. At least one air purifier we’ve tested with a HEPA filter was so disappointing in other respects that we made it a Don’t Buy. 

A HEPA filter won’t tackle odours or gases either – for that you'll need a carbon filter. 

Carbon filter

For unpleasant smells and gases, including VOCs (volatile organic compounds) from common household products such as cleaning products, you’ll need a carbon filter. 

This is also sometimes called an activated carbon filter or a charcoal filter. 

Increasingly, most air purifiers, and a few dehumidifiers, come with a carbon filter. But don’t solely rely on it: instead, ventilate your home regularly, as we said before.

Automatic mode and air-quality sensors

Many air purifiers have air-quality sensors. If left on automatic mode, these machines will sniff out pollutants and spring into action as needed. If you've just sprayed deodorant, for example, the air purifier will detect a change in the air quality and work harder.  

Often these air purifiers will also give you information on the quality of the air in the room (based on their estimation), in the form of a coloured light on the air purifier display. If you've got a smart air purifier (an air purifier that is internet connected) you may also get more detailed information sent to your smartphone app. 

Do you suffer from a pollen or dust allergy? Find out which models are best at removing pollen and dust from the air: see all our air purifiers.

woman breathing in

Air purifier timers

Most air purifiers come with a timer, which you can use to set your air purifier to come on or turn off after a certain number of hours. That could be handy if you routinely change the settings at the same time each day. You might, for example, want your air purifier to run at high fan speed all day if you're out at work, and then at a lower speed in the evening and at night. 

If you're going to use your timer, it's worth bearing in mind that you can't just set an air purifier to run for a few hours each day and expect it to make much difference to your air quality. Air purifiers are designed to run pretty much constantly. The more often air passes over the air purifier filter, the cleaner the air in your room will be. 

Humidification or heater functions

A couple of air purifiers have other functions, such as heating or humidification. 

The Dyson HP04 Pure Hot+Cool Purifying Fan Heater (£549), for example, can heat or cool a room, while the Dyson Pure Humidify+Cool (£599) can also humidify. 

Dyson is a famous brand, but our tests have shown time and again that big name is no guarantee of a great product – check our Dyson air purifier reviews before you buy.

Smart air purifiers

Smart air purifiers tend to be more expensive, as you'd expect. These can be controlled from a paired smartphone.

Some of the accompanying apps offer other useful features: information about the air quality levels in your home, reports on the outdoor air quality in your area and reminders to change the filter, for example. 

Smart air purifiers we've tested include the Blueair 605, Blueair Classic 405 and the Philips AC3829/60 2-in-1 Air Purifier and Humidifier

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

Air purifiers for coronavirus

You might be wondering if an air purifier can protect you from coronavirus/Covid-19, given there's increasing evidence to show that the virus can linger in enclosed indoor spaces. 

The government says that: 'Bringing fresh air into a room and removing older stale air that contains virus particles reduces the chance of spreading Covid-19. The more fresh air that is brought inside, the quicker any airborne virus will be removed from the room. Ventilation is most important if someone in your household has Covid-19 or if you are indoors with people you do not live with'. 

It's important to remember that:

  • Running an air purifier is not the same as ventilating your home with fresh outdoor air. As we mentioned earlier, you'll need to close the window to the room the air purifier is in for it to work most effectively. Opening a window to introduce fresh, outdoor air is more ideal
  • Air purifiers' effectiveness depends on many factors, including the technology involved, the environments they're used in and how well they're maintained
  • There's currently no scientific evidence to show that an air purifier can make your home safe from Covid-19, and existing tests with air purifiers in a controlled lab environment can't be taken as representative of real-world use
  • Covid-19 can also be spread through other routes, which an air purifier can't tackle.

The key thing is to follow the latest NHS guidance. If you don't bring someone with Covid-19 into your home, you won't need to worry about contracting Covid-19 from the air there. 

We do know that increased ventilation is a good thing in general when it comes to indoor air quality. And, where it’s not possible for you to properly ventilate a room in your home, due to poor outdoor air quality, a good air purifier can help. In that context, a good air purifier could clean the air to some extent and potentially help with breathing issues by reducing the level of allergens.

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. Most of our Best Buys air purifiers are in the £300 to £400 price bracket. 

But spending this much doesn’t guarantee you’ll end up with a great machine. One of the models we've made a Don't Buy is sold for £320 at the time of writing, which is mid-priced for an air purifier. 

How much does an air purifier cost to run?

Obviously the cost of running an air purifier will depend on a number of factors, including how much energy it uses, how often you run it and how much you're paying for energy. 

As a rough guide, though, if you were to run your air purifier for 12 hours a day, every day, it could cost you between £20 a year and about £160 a year. That's based on the assumption that electricity is 14.4 pence/kWh (kilowatt-hour).

Are there quiet air purifiers?

Some air purifiers have a specific night mode, which reduces the fan speed and dims any lights so that the machine doesn't keep you awake. If you're not planning to run your air purifier in your bedroom, then you might not be too worried about this. 

If you are, though (if you have allergies that interfere with your sleep, for instance), then you can use our air purifier reviews to find the ones that are genuinely quiet on their lowest or night setting versus those that aren't. 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. 

If you've already bought an air purifier with a not-so-quiet night or low fan mode, try running the air purifier in your bedroom all day, with the doors closed, and switch it off at night. That way, at least the air in your room will be much cleaner at the point you try to sleep.

man sleeping

The quietest machines do a very good job of keeping noise to an absolute minimum, both on the lowest and highest setting. 

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.

What is a HEPA filter?

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

You’ll also need to clean and replace any filters periodically (check the manufacturer instructions to find out how often). A clogged-up filter won’t be very effective at trapping particles. So when you’re buying an air purifier, it's wise to check if replacement filters look to be easily available.

Some machines have a filter-replacement indicator light, which shows when the HEPA filter needs replacing. And some send a notification to your smartphone app. 

New HEPA filters can vary in cost from about £20 to more than £50 depending on which air purifier you buy. 

hepa filter

How to make air purifier HEPA filters last longer

Manufacturers generally recommend you change your filter every six months, as once it's clogged up it won't be much use to you. That depends on how often you use your air purifier, though. If you don't use it every day, your filters might last a bit longer. 

With some machines (not all), you can also clean the filters to extend their lives, which will save you money. Always follow the manufacturer instructions. If you do vacuum your filter, go gently. Vigorous vacuuming can damage the delicate fibres. And do it outside, to avoid reintroducing captured allergens to your home.

What is an air ioniser? 

Instead of using a fan or filter to purify the air, an air ioniser does it by electrically charging air molecules.

An ioniser creates negative ions (a charged particle) and pushes them into the air where they can attach to positive ions (dust, allergens etc). After bonding together, the particles become too heavy to float and will drop to the floor or nearest surface, to be cleaned away.

Do air purifiers release ozone? 

Ozone can react with pollutants to alter their chemical composition. If you have a lung condition, ozone can lead to breathing difficulties, wheezing and coughing. Even if you're healthy, ozone can irritate your airways. 

You don't need to worry about an air purifier which uses a HEPA filter alone to clean the air. However, ionizing air purifiers, or products that use UV lights, could give off ozone because of their electric charge. If you can, look for one that states that it does not create ozone. You should actively avoid any that describe themselves as 'ozone generators'.