Choosing An Air Purifier

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John Wilton-Davies
[image is of the new Blueair DustMagnet, coming very soon]

So, you’ve done your research and decided you need a purifier. But how do you choose the right one?

The internet is full of advice - both good and terrible - but unless you’re an expert you don’t know which. And if you are an expert you don’t need the advice in the first place. So here’s our quick guide to get you started.

What do you need it to do?

There are 2 main types of air pollution: particulate (soot, dust, pollen etc); and chemical (sometimes called VOCs). You need a different type of filter to remove each - not not necessarily a different purifier - you can often fit different filters into the same purifier.

There are several different filter technologies but the most established and, probably, the most effective are a high efficiency particulate filter (HEPA) for, yes you guessed it, removing particulates, and activated carbon filters, for removing airborne chemicals.


Most good purifiers now come with HEPA filters, meaning they’ll do a good job of removing particulates. Good carbon filters are expensive and many purifier manufacturers now supply filters as standard that are marketed as carbon filters but, in reality, will not be at all effective. The amount of carbon in the filter is important (for example the MobileAir filter for cars contains 900g of activated carbon), and many such filters include only a spray-on carbon film (with perhaps 20g of carbon) that will be fairly useless. But it does allow the filter to be described as ‘carbon’, making your life more confusing. A good particulate filter is what you'll need for removing airborne viruses, including Covid-19.

How big/powerful does it need to be?

Most retailers describe purifiers in terms of the size of room it’s suitable for. Treat this with a big pinch of salt..

What’s important is the relationship between the volume of the room it’s going in, and the rate at which it cleans the air - known in the trade as CADR, or Clean Air Delivery Rate. You can use any size purifier in any size room and it will do something useful, but to understand how much it will do, find the CADR (it’s usually mentioned by the better manufacturers) and divide by the approximate volume of the room - with everything in cubic metres. The number you’re left with if the ‘number of air changes an hour (ACH)’ the purifier will give at maximum power.

The usual advice is that 5 ACH is good, and up to 10 is ideal if the room has many occupants and you’re worried about Covid. But, we’ve put maximum power in italics for a reason. Purifiers make noise, and the faster they’re cleaning the air the more noise they make. If you’re going to use the purifier in your bedroom at night, or in a quiet space, or when you’re watching TV, you don’t want a lot of distracting noise. So you’ll end up either turning the purifier down to make it quieter or, worst still, turning it off.

So you’re better choosing a purifier that is both over-powered (e.g. gives you 7-8 ACH if you really want 5, so you can run it at a lower, quieter setting) and is fundamentally quieter than most (which is one of the reasons we love the Blueair range). Unfortunately a more powerful purifier costs more, leading us to…

How much should I pay?

Please, please, please don’t start your decision process with price. A noisy, ineffective model that’s cheap is a total waste of money. Make sure it’s going to have all the attributes you need (and the right filters, air cleaning rate and noise levels are absolutely key), then look at prices.

As a guide - for a particulate only machine for a smaller bedroom, expect to pay around £100-£150. For a large open-plan living area with a good chemical filter too, you should be looking at £600 - £900.

Don’t assume a well-known brand name is going to be better. We often end up replacing customers ‘well-known’ brand with cool design with a quieter, more cost-effective alternative. Try not to pay for extra gadgets you may not use - perhaps UV sterilisation -  although some are useful, such as timers, automatic sensors. And definitely don’t assume that the more expensive the better. At Plain Air we’re always happy to give you advice, whether or not you buy something from us.

How many do I need?

Ideally, one per room you want to keep clean. A small unit in each room is generally better than a large one trying to clean several rooms but your budget will always be the priority. Again, it’s far better to get one good purifier that you’ll keep using than two less effective, noisier ones than you’ll end up just turning off.

Make it worthwhile…

…by using them every day. Unless you’ve got some decent air quality monitors just assume that the air quality is poor and use the purifiers all the time. And replace the filters when needed - many purifiers will tell you when they think it’s time for a change, and if you buy one from Plain air, we’ll remind you. Don’t treat a purifier like an exercise bike at Christmas - consider it a long-term investment in your health. When you’re in the room/house/office leave the purifiers turned on (at a level where the noise doesn’t bother you) all the time.

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