To get the most out of any of the air purifiers Wirecutter recommends, you need to set them up properly, operate them properly, and perform very occasional maintenance. None of this is hard. But all of it is important. Most especially:

Remove the filter wrappers! Most air purifiers arrive with the filters installed in the machine—sealed in plastic wrappers. Leave aside the complete senselessness of manufacturers hermetically sealing things whose entire job is to deliberately get dirty. The fact is, many first-time purifier owners don’t realize they have to open up their new machine and unwrap the filters. And that means many people have gone months or years running an air purifier that’s doing nothing. You can find three pages of comments about this topic on the Amazon listing for our top pick, the Coway AP-1512HH Mighty, alone. We know of at least one Wirecutter reader and one Wirecutter staffer who didn’t realize they needed to remove the plastic before turning their purifier on. And during the 2018 California wildfires, a Facebook group that another staffer belongs to revealed something like a dozen people who had made the same mistake. So if you get a new air purifier, open up your machine, and if the filters are indeed wrapped, unwrap them!

The rest is fairly obvious, but worth a quick recap.

Give your purifier room to breathe. Try to place the air purifier at least 18 inches from the wall and any furniture, ideally near the midpoint of the room you’re using it in. It needs to be able to draw air in, unobstructed, to catch particulates and continue circulation.

One purifier per room is best. Purifiers work best in a contiguous space. If you want to clean the air in both the living room and a bedroom, for example, it’s best to get a purifier for each room or to move a single purifier around with you.

Oversized is better than undersized. It’s better to have “too much purifier” than not enough. Manufacturers typically base their room-size recommendations on tests with the machines set on high—but high is usually too loud to watch TV or sleep with. Purifiers rated for spaces larger than the one you plan to use them in can operate at lower, quieter speeds. All our picks are sufficiently oversized that running them on their “quiet,” medium settings will keep the air clear in the rooms they’re sized for.

Keep your purifier running. We recommend running air purifiers 24/7 on their highest “quiet” setting—usually medium. (By “quiet” we mean below 50 decibels, though on many machines the medium setting produces much less noise, in the low 40s.) Put another way, we recommend avoiding the “automatic” setting that some purifiers offer. That’s for two reasons. First, there’s no way of telling whether the sensor these machines use to determine their automatic on/off cycles is working properly. Second, depending on what a manufacturer determines as “poor enough” air quality, an automatic setting may let the air in your home get quite laden with particulates before kicking the purifier on.

Under known bad-air conditions, such as during a nearby wildfire, we recommend running purifiers on high for an hour and thereafter on “quiet”/medium. Our test results confirm this advice.

Close doors and windows. You should keep the doors and windows closed when you’re using an air purifier. A draft or an open door can draw unfiltered air into a room faster than the purifier can deal with it. (Normal in-and-out foot traffic isn’t an issue; just close the door behind you.)

A stack of air purifier filters that are dirty.
Your purifier’s prefilter (top of the stack) captures big stuff like pet hair and needs to be cleaned monthly. Photo: Tim Heffernan

Clean the prefilter monthly. For optimal performance, vacuum, wipe down, or rinse off the prefilter (it looks like a window screen or plastic netting) every month or so. The prefilter catches larger particles such as pet hair, and keeping it clean helps the HEPA filter work unimpeded on fine particles.

Schedule filter replacement. It’s easy to forget the occasional obligation of replacing your purifier’s filters, so set a calendar reminder. Purifier manufacturers typically recommend annual replacement; check the manual to be certain. We think it’s wisest to follow the manufacturer’s recommendation, but we have also found that HEPA filters continue to perform almost like new even after a year of continuous use—so if you do blow past the annual deadline, it’s not a crisis.