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How to buy the best air purifier

Our expert explains what to look for so you can pick the best option for cleaning the air in your home.

air purifier in bedroom

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? How effective will it be at actually cleaning the air? We'll help you make sense of your options so you can make the right choice for your home.

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How does an air purifier work?

An air purifier usually works by using a fan to draw in air from the room and force it through a set of filters, which trap pollutants like dust, pollen, pet dander, smoke particles, various chemicals, mould spores and germs. The cleaned air is then blown back out into the room. Air purifiers usually have air quality sensors and other features to help them perform this task more effectively.

Some air purifiers work differently, by pumping charged particles (ions) into the air, which then attach to pollutant particles and break them down or make them drop out of the air.

Do you 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, like 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 asthma and allergies, particularly to dust and pollen.
  • To help keep the air clear of bacteria and viruses if you have sick people at home.
  • 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.

Can an air purifier help clear bacteria or viruses?

Likewise, a purifier can also assist with removing viruses, bacteria and other nasties such as mould spores. There are some limitations though – see our article on how air purifiers deal with viruses and bacteria.

Can an air purifier keep the air fresh in your home?

It's usually recommended that the air in a room should change (be replaced by fresh air) several times per hour, to prevent the build-up of carbon dioxide, odours, moisture and other pollutants. The simplest way to do this in most cases is through natural ventilation: opening doors and windows and letting in the breeze.

When that's not possible, such as in small rooms with poor ventilation, or when the outdoor air is too hot or cold, or too smoky, then an air purifier will certainly help. But it's unlikely to achieve the same level of air change in the long term, and it won't remove a build-up of carbon dioxide, or introduce more oxygen in the same way that good ventilation can.

Does an air purifier remove the need to dust your home?

Alas, however good the air purifier is at removing dust and other particles from the air, there's always more that settles on the furniture and the floor. Dusting, vacuuming and mopping will still be a necessary chore.

What is the Clear Air Delivery Rate?

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'll 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.

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, carbon and more

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.

Carbon or charcoal

Carbon or charcoal filters are said to be good for trapping odours and VOCs such as formaldehyde.

Ozone 

Ozone filters are said to be good for removing odours. But at low levels they've been shown to be ineffective at removing air pollution, and at high levels they can cause breathing irritation. We recommend you avoid these models.

Ionic or ionisation

Ionic or ionisation filters are believed to be good for removing fine particles such as dust and smoke, but ionisation of air can produce ozone (see above).

Ultraviolet (UV) sterilising

UV sterilising filters are 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'll 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. That said, you may be able to extend the life of the HEPA filter by gently brushing or vacuuming its surface to stop it clogging up with dust.

Some models have separate filters (HEPA, pre-filter, carbon etc.) which can be replaced separately as needed. Others have an all-in-one filter cartridge which can be more convenient, but may mean you're replacing the whole lot when only one of the filter types actually needs replacing.

In some cases replacement filters can be well over $100 per year

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.

Replacement filter costs can add up quickly – see our air purifiers review for the filter prices and estimated annual costs of models we've tested. In some cases these can be well over $100 per year. If you're able to run the air purifier only occasionally (such as only on smoky or high-pollen days), the filters will of course last longer and your costs per year will be less. However, if you're very sensitive to air pollution, you might need to run the air purifier all year round.

How much do air purifiers cost?

Air purifiers generally cost about $200–500 but can go over $1000. Replacement filters and filter sets typically cost from $40–100+, depending on the brand and model of air purifier.

Environmental impact of air purifiers

While air purifiers are all about providing clean air for your home, they unfortunately aren't always so eco-friendly towards the environment as a whole. There are definitely some concerns around air purifiers when it comes to sustainability.

Disposal to landfill

As we describe above, air purifiers have filters that need replacing, in some cases a few times per year. Once a HEPA filter is used up, there's no option but to replace it, and in most cases the old filter can't be recycled. HEPA filters are usually made of a variety of materials including natural and synthetic fibres and a plastic frame, and it's unlikely to be cost-effective for a recycling plant to try to extract anything. And at the end of their life, they will contain a lot of pollutants such as dust, pollen and chemicals. All these will end up in landfill with the filter.

While some filters such as pre-filters and charcoal filters can be washed and reused, eventually they will need to be replaced too, and again, the old filters are likely to go to landfill. But it's worth checking for any disposal instructions; some may be made of recyclable plastic types, for example.

And the air purifier itself (like many home appliances) is also unlikely to be accepted by most recyclers, so at the end of its life, it will usually go to landfill too. Again, check the instructions for any recyclable parts.

In our recent tests, we've found that models from Beurer, Kmart, Winix, Homedics, IKEA and Dyson were packed in cardboard, which can go into household recycling, while others were packed in polystyrene or polyethylene foam. 

Energy efficiency

Air purifiers generally don't consume a lot of electricity, and even if left running all the time, the energy usage per day is likely to only be a few cents worth. Nevertheless it is worth thinking about turning the air purifier off when it's not really needed. That will also prolong the life of the filters and the appliance itself.

We rate each model in our review for its comparative energy efficiency. A poor rating here doesn't necessarily mean that the unit uses a lot of electricity, but it does mean it doesn't use that electricity as effectively (for better air cleaning performance) as the higher rated models.

Features to look for

Sensors and timers

Most air purifiers have sensors to determine how much pollution is in the air around them, along with other measurements such as indoor air temperature and humidity. Usually they'll display this information on the unit or (for Wi-Fi connected models) in an associated app, perhaps as a detailed particle count, or as a simple coloured indicator (such as green for good and red for heavily polluted air). 

Some can be set to activate themselves automatically once pollution reaches a certain level, which can be handy if you'd like the purifier to maintain good air quality without the need to keep running 24/7. 

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.

It can be very interesting to see just how much dust or smoke is in your home's air, and the sort of activities that add to pollution. For example, frying food on a gas cooktop can rapidly put out a lot of pollution (even when you don't burn the food!). Spraying insecticide, using cleaning fluids and painting will also add chemicals and fine aerosol particles to the air. 

Leaving the purifier to run on automatic, so that it adjusts its speed to suit the level of pollution, can be useful too – hearing it rev up can be an indication that there is smoke or other pollution getting into the home.

Fan

Look for an air purifier 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 it, 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 air purifiers can be connected to your home's Wi-Fi network and controlled via a smartphone app, which 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 air purifiers 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 while 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.