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Black Friday: Why some deals on air purifiers might be too good to be true

The things to look out for when buying an air purifier this Black Friday – and how to avoid ending up with a dud

Black Friday: Why some deals on air purifiers might be too good to be true

Air purifiers can be useful gadgets for clearing the air in your home if getting more natural ventilation isn’t an option. With Black Friday around the corner, you might be tempted to buy one for a seemingly great deal: but watch out for deals that aren’t as good as they seem. 

If a Black Friday deal seems too good to be true, then sadly it probably is.

We reveal the key things to look for in an air purifier so you can shop safe in the knowledge that you’re buying a quality product.


Just want to know which are the best? See which air purifiers are worth the price from our list of Best Buy air purifiers.


Air purifier in a room

Should you buy an air purifier on Black Friday?

An air purifier should never be your first port of call if you’re worried about indoor air pollution. First, you should try ventilating naturally, by opening windows more frequently and using cooker hoods and extractor fans.

And you should minimise activities that generate indoor air pollution such as burning scented candles and spraying scented toiletries and cleaning products.

If you can’t easily do that, though (say, you live on a a very polluted main road or suffer from hay fever), an air purifier could help get the air in your home cleaner. So, should you buy an air purifier on Black Friday?

The trouble with good-looking deals

Just because there’s a huge price slash on a product, that doesn’t necessarily mean you’re getting a bargain.

Last year, we found that there were many air purifiers on sale around Black Friday from obscure brands which we’d not tested because you’d rarely come across them. We also saw models on sale which had performed badly in our tests. We didn’t see all that many high-performing air purifiers on sale – though it’s possible that might change for 2021.

You should also watch out for adverts claiming that air purifiers will protect you from coronavirus.

It’s important to understand that an air purifier alone is unlikely to protect you from Covid-19, and there are more effective preventative steps to take if you’re concerned about catching it.

For more on this, see our advice on why you shouldn’t rely on an air purifier to protect you from Covid-19.

Man browsing deals online

What to look for when buying 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 0.3μm (micron) in diameter.

Keep an eye out for filter with marketing names such as HEPA-type, HEPA-style and so forth as they might not conform to the same criteria.

A HEPA filter makes it more likely that an air purifier will be good. While we’ve reviewed most of the air purifiers on the market, if you’re buying one that we haven’t reviewed, buy one with a HEPA filter.

Do note that a HEPA filter doesn’t guarantee that an air purifier will be good; there are other aspects to an air purifier that might make it poor. At least one air purifier we’ve tested with a HEPA filter was so bad that we made it a Don’t Buy air purifier.

A HEPA filter won’t tackle odours or gases either: more on that below.

You’ll also need to clean and replace any filters periodically. A clogged-up filter won’t do much to filter out particles. So, when you’re buying an air purifier, check if replacement filters are easily available.

If we discover that the replacement filters needed for a Best Buy air purifier aren’t available for a long period of time, we remove our Best Buy recommendation from that model.

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 come with a carbon filter. But don’t solely rely on it: instead, ventilate your home regularly. Use out guide on reducing pollution in the home to find out what else you can do to improve your indoor air quality.

Fan speeds and settings

Many air purifiers come with a timer, which you can use to set your air purifier to turn on or off after a set number of hours. That could come in handy if you routinely turn it on or off at the same times each day.

You will also come across night mode: this will lower the fan speed and dim any lights when you’re trying to sleep. If you’re not planning to run your air purifier in your bedroom overnight, you might not be too worried about this.

If you do, though (let’s say you have allergies that interfere with your sleep at night), then you can use our air purifier reviews to find out which ones are genuinely quiet and discreet on their lowest or night-time setting, versus which ones aren’t.

Most models will have at least three fan speeds, allowing you to whack up the speed when you know that you’ve just generated pollution, and lower it again when you want some peace and quiet. Some will come with a much larger number of speed settings though, which is a nice bonus but not an essential

Automatic modes and air quality sensors

Many air purifiers have an auto mode, meaning they’ll detect the level of pollution in the air and spring into action when they need to, without you having to manually adjust the settings. That’s a useful feature to have, as it saves you having to keep thinking about it yourself

Some of these also report on the pollution they’ve detected, either sending the information to an app on your smartphone or displaying it on a screen on the machine itself.

Air purifiers line-up

Ready to get stuck in to the best seasonal bargains? Check out or Best Black Friday deals. Plus, get the insider tips and tricks with our Black Friday insider’s guide.


Which? air purifier reviews

Only the absolute best models on the market, as proven by our independent lab tests, earn our Best Buy recommendation.

Our tests measure the clean air delivery rate (CADR) of each machine: how quickly an air purifier can trap dust, pollen and smoke particles from the air.

We use CADR to compare between air purifiers because it is an internationally recognised test standard. Dust, pollen and smoke are common household allergens and represent a range of particle sizes.

We can also tell you for each air purifier:

  • How noisy it is on full and low power
  • Whether it uses energy efficiently
  • Whether the filters are easy to take out, clean and slot back in
  • How easy the smart app is to use, if there is one
  • Whether its smart app is secure.

We’ve reviewed more than 40 air purifiers. To find out which ones are Best Buys and Don’t Buys, head to our air purifier reviews.

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