What to look for in an air purifier

The most important spec to consider when looking at air purifiers is how efficiently the device filters air particles. You'll see this demonstrated as a high percentage like 99.97%, and again by the kind of filter that is used. 

The percentage references the amount of particles and bacteria that the filter is capable of removing. The higher the number, the more efficient the filter is. These percentages also align with the filtering class of the filter. For air purifiers these are either EPA or HEPA, standing for efficiency particulate air [filter] and high efficiency particulate air [filter], respectively. 

As you may have guessed, HEPA filters are better at filtering out particulate matter from the air. At their best, HEPA14 filters remove 99.995% of particle matter, while EPA12 remove 99.5%. Both are high numbers, but the difference between those percentages is important. That extra 4.95% captures PM2.5 particles like mould spores, smoke, pollen, and bacteria, which have been linked to ongoing health effects.

Some air purifiers come with additional filters like a pre-filter and an activated charcoal filter. These extra filters won't do much more to remove dust and dander from the air, but they can help with the longevity of the HEPA filter and eliminating odours.

Like heaters, and air conditioners, air purifiers all have a coverage spec which tells you the largest space it can efficiently be used in. While using a more powerful purifier than your space requires won't cause harm, using a smaller one means it has to work harder and be on for longer. Cheap air purifiers are fiends for a small coverage area, so if you're contemplating one from Ikea or Kmart chances are you'll have to have it running 24/7 to have any palatable effect.

Coverage numbers are usually in metres squared, and are generally accurate in rooms with ceilings up to 2.4m high. If you've got higher ceilings, or particularly leaky windows and doors you'll be better off opting for the more powerful device.

Air purifiers don't have to be super high-tech, they're like fans, if you turn them on they'll usually do the trick. In saying that there are a handful of features that you should look out for, and others that are a boon to have.

First up you should always look for an air purifier with air quality readings built in. Most use a basic traffic light system to demonstrate air quality - red = bad, orange = okay, green - good - but others have more indepth data. Which one you prefer is up to personal taste, but you'll want to make sure they actually have one so you can see how well the device is working for you. Alternatively you can buy air quality monitors seperately, but that is an extra expense that is easily avoided.

After that you may want to keep an eye out for features like scheduling, auto-off functions, and timers. While these aren't neccessary for a machine to work well, they're nice little additions. You may also want to look into whether the device needs a companion app, and whether that app is actually useful or not. Spoilers: many of them aren't.

Apart from the obvious outright price, make sure you look into the ongoing running costs of the air purifier. Consider the cost of filter replacements, the warranty period, any repair pricing, and how much electricity the device uses.

The most pressing out of these is the filter replacement price. You'll usually have to replace the HEPA filter every six months to keep it running at top efficiency, and since filters aren't one size fits all it can be hard to find one that fits. Generally you're going to be better off buying these direct from the retailer, and in some cases they can get pricey. Acerpure for example charges up to $130 for replacement filters, while Kmart charges $29.

It is also worth considering the wattage of the device to figure out how much running it will cost you. Usually air purifiers will cost you less than $0.01 per hour to run, but if you're opting for something fancier like Dyson's Hot+Cool Air Purifying Fan then the price can sky rocket. In heater mode the Dyson uses 1500W, which costs about $0.21 per hour according to the latest electricity cost data. Over time that can add up.