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How to buy the best air purifier

Picking the best option to clean air in your home.

air purifier on yellow background

Choosing a good air purifier can be a tricky business. Do you really need one? If you do get one, what size should it be, what features are important, and how effective will it be at actually cleaning the air? We'll help you make the right choice for your home.

Note: We currently have an interim review of six air purifiers and a more comprehensive test in progress, which we aim to publish in March 2020. Be the first to know when the full review is available, sign up for our newsletter.

Do I need an air purifier?

Indoor air quality is important – after all, we spend a large part of our lives inside our homes breathing that air. It's easy to assume that pollution is really an outdoor problem, but that same air containing traces of vehicle exhaust, airborne dust and pollen, smoke and other pollutants comes into our homes. Other sources of pollution are already inside the home; for example, household dust, cigarette smoke, volatile organic compounds (VOCs) emitted from paint and the foam inside sofas and mattresses, pet hair and dander.

Indoors, pollutants have less chance to simply blow away, and can build up over time. All these types of pollution have the potential to cause irritation to your breathing, eyes and skin.

In many cases you can address most of these problems with regular vacuuming, mopping, and airing your home when the outside air is clear, so an air purifier isn't always an essential appliance. However, they can be useful in many situations. 

The main reasons to own an air purifier:

  • To help with allergies, particularly to dust and pollen
  • To help with asthma
  • If you smoke inside your home
  • If your neighbourhood has particular pollution problems, such as being near a major road or in an area affected by bushfires

Note that air purifiers can only clean dust and other pollutants from the air. Dust on the floor or furniture still needs to be vacuumed or wiped up.

Can an air purifier help clear bushfire smoke?

Yes, a good air purifier can help clear the air inside your home of smoke and smoky smells. You will need to close all doors and windows to stop more smoke getting in, at least for the room you want to purify. A purifier with a HEPA filter is your best option for filtering smoke.

CADR rating

The Clean Air Delivery Rate (CADR) is an industry standard measure of the volume of air that the air purifier can clean. It's expressed in cubic metres per hour (or cubic feet per second). The bigger the number, the better.

The CADR test is done in a small room (a square room about 3.4m per side and 2.4m high), with the purifier unit in the centre of the room and set to its highest speed setting. It's a 20-minute test, done separately for each of three pollutants (dust, tobacco smoke and pollen), so you will see some models stating their CADR rating for each type.

While CADR is a useful way to compare performance between models, it's not necessarily a good indicator of how an air purifier will perform in your own home. You're more likely to have the air purifier down one end of the room or in a corner, and you won't always be using the highest speed settings. Also, the CADR test doesn't measure the removal of other pollutants such as VOCs and very fine particles.

Dyson has developed its own test method, known as POLAR, which is intended to test performance in a more typical set-up. This test is in a larger room, with the air purifier in one corner, and can be used for a wide range of pollutant types.

All about filters

HEPA filtration

Testing by our counterpart consumer organisations around the world has found that HEPA filtration is the most important feature for an air purifier.

HEPA stands for high-efficiency particulate air. It's a very effective type of filter which traps very small particles, invisible to the naked eye. Generally, HEPA filters can trap at least 99.95% of dust, smoke, mould and other particles in the air, down to a tiny 0.3 microns in size.

HEPA filters are common in good-quality vacuum cleaners and you should look for HEPA filtration in an air purifier too.

Other filters:

Carbon or charcoal

Said to be good for trapping odours and VOCs such as formaldehyde.

Ozone 

Said to be good for removing odours. But at low levels it's been shown to be ineffective at removing air pollution, and at high levels it can cause breathing irritation. We recommend you avoid these models.

Ionic or ionisation

Said to be good for removing fine particles such as dust and smoke. However, ionisation of air can produce ozone (see above).

Ultraviolet (UV) sterilising

Said to be good for killing viruses, bacteria and mould spores. But UV light takes at least a few minutes to kill germs, and it's unlikely any germs passing through the air purifier will be exposed to the UV that long. Don't rely solely on a sterilising filter if this level of cleanliness is important for you.

Filter cleaning and replacement

An air purifier may have multiple filters (including the HEPA filter) and these will need regular cleaning or replacement. It's more economical to be able to wash and reuse a filter than to have to buy replacements each time, especially if you will be using the air purifier frequently. Most pre-filters and carbon filters can be washed and replaced; HEPA filters are not usually washable and you'll need to factor in buying replacements for these.

A good air purifier will have a warning indicator to let you know when it's time to clean or replace the filters. Alternatively, the instructions might simply specify to replace the filters after a certain period of time, such as every six months. But check how the replacement time is calculated; it might assume that the purifier is run all day every day, so if you use it less often, you shouldn't need to replace the filters as frequently.

Features to look for

Sensors and timers

An air purifier with air sensors can monitor the level of indoor air pollution and display this information to you. Some can be set to activate themselves automatically once pollution reaches a certain level. This can be handy if you'd like the purifier to maintain good air quality without the need to keep running 24/7. For example, if you live near major roads which lead to high pollution levels only at certain times of the day, or during springtime when pollen counts can vary significantly from day to day.

In the absence of automatic sensors, a simple timer function can be useful, to set the unit to run at certain times of the day.

Fan

Look for a model with a good range of fan speeds. You want powerful air flow when you need to clean a room's air quickly, but a gentle air flow for use at night in a bedroom. An oscillating action is useful for covering more of the room space.

If the purifier doesn't have a good range of fan speeds (or no fan at all) then it's worth considering using a regular fan in the same room, such as a pedestal or ceiling fan. It's important to have good air circulation while the purifier is running; otherwise, it can end up just cleaning the air around itself, leaving pollutants in the air in other parts of the room.

Be aware that the air purifier might be quite noisy on its highest settings.

Wi-Fi apps and remote controls

A remote control is great for convenience, but not all models have them. Some models can be connected to your home's Wi-Fi network and controlled via a smartphone app. This can serve as an alternative to a dedicated remote control. Some models, such as Dyson's Pure Cool and Pure Hot + Cool (but not currently their Pure Cool Me range) also give you access to collected data from the air purifier, allowing you to see what sort of pollutants it's been removing from your home.

Portability

Air purifiers can be fairly heavy appliances – they can weigh about 10kg or more – so if you plan to move the unit between rooms, check that its weight is manageable. Wheels and carrying handles can make moving easier.

Room size

Most models will have a recommended room size. It may be worth getting a model that's rated for a larger room than you plan to use it in. That can mean the purifier will clear the room's air faster on its highest setting, but still comfortably keep the air clear on its lowest and quietest speed (good for when you're trying to sleep).

Alternatives to air purifiers

The main alternative to buying an air purifier is to keep your home clean of dust by wiping down furniture regularly, and vacuuming your floors thoroughly. Use a vacuum with HEPA filters to make sure you aren't just blowing dust back into the room as you vacuum. Regular mopping of hard floors is a good way to remove more dust and pollutants. Lastly, regularly air the house when the air outside is fresh and clear.

Do air conditioners have HEPA filters?

An air conditioner can help filter out some dust and pollen from the air, but won't usually remove smoke, very fine particles or VOCs. HEPA filters can't practically be fitted to split-system or ducted air conditioners, because air conditioners have to deliver quite significant volumes of air flow into the room, and would need massively powerful fans in the indoor unit to force that amount of air through the very tight weave of a HEPA filter. That said, some recent models of air conditioner include extra filters or features such as ionising or photocatalytic filters, which should help to trap fine particles such as allergens, mould spores and so on. While they are unlikely to be as effective at smoke removal as a dedicated air purifier, they should still help (though note that as mentioned above, ionisation can create small amounts of ozone).

Costs

Air purifiers generally cost about $200 to $500 but can go over $1000. Replacement filters and filter sets typically cost from $30 to $100+, depending on the brand and model of air purifier.

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