If buying an air purifier is the first step to breathing clean air, then the second step is knowing the best way to use the air purifier! Here are the 4 most important things to know about how to use an air purifier, from where to place your air purifier, to when to turn it on. All this—based on data, not intuition.
1. Note Down The Date of Purchase
HEPA filters have a lifespan. And unfortunately, the best way to judge when to replace filters is by the date. When I first started testing purifiers, I thought I’d be able to judge based on the color of the HEPA. However, the data showed that the HEPA remained effective long after it had turned black. Color is an unreliable indicator of when to replace a filter.
Although there’s a bit of imprecision, at least it’s easy to do and backed by data: Note down the date you first used the purifier and replace the filter after the specified number of months.
The numbers above are calculated assuming the purifier is on 8 hours a day. You can adjust the number of months based on the number of hours you use the purifier each day.
2. Keeping Your Rooms Well-Sealed
One way to increase the effectiveness of your air purifier is to make sure the room is well sealed. The easiest way to improve your home’s seal is to use insulation tape to plug up gaps around windows and doors.
The Downside of A Well-Sealed Room
However, there is a cost. The better sealed our homes are, the more the CO2 we breathe out will build up. That’s not a big deal if there aren’t many people in the room, but if there are several people in the room, CO2 can reach levels that will make people drowsy.
Some other pollutants coming from indoors will build up too. One example is formaldehyde coming from new furniture and flooring. Smart Air’s real-world tests show that activated carbon filters will reduce formaldehyde and other VOCs.
If you want fresh air, our tests have found it still possible for purifiers to clean the air when a window is open. Of course, with a window open or a poorly sealed room, you would need to use a stronger purifier and replace the HEPA sooner.
3. The Best Way to Place Your Purifier
Many people place their purifiers against the wall because it’s out of the way and looks nice. But that’s not best place for them. We tested it, and found the best place to put an air purifier is at least 10cm from the wall.
Learn more: How best to position your air purifier »
4. You don’t have to run your purifier all day
Some purifier companies suggest running the purifier 24 hours a day, even if you’re not at home.
Smart Air’s tests in real-world homes found that purifiers like the DIY Cannon can reduce particulate by 80% in a 13.5m2 Beijing room in just 20 minutes. This means you don’t have to waste the energy or HEPA lifespan when you’re not at home.
Can I Turn My Purifier Off at Night then?
The flipside is that we have to keep purifiers on at night. Some people have the intuition that if the purifier cleans the air, they can turn it off, keep the windows closed, and the air will stay clean all night. However, we tested this by turning a purifier off in a real Beijing apartment and testing how long it took for the air to get polluted again.
The data showed that particulate levels returned to 50% of baseline pollution levels after just 15 minutes and back up to 100% after 80 minutes. Thus, we need to run our purifiers all night. (Side note: that’s also part of the reason auto modes like on the Xiaomi model frequently leave air at unsafe levels.)
How I Protect Myself
Smart Air is a certified B Corp committed to combating the myths big companies use to inflate the price of clean air. Smart Air provides empirically backed, no-nonsense purifiers and masks, that remove the same particles as the big companies for a fraction of the cost. Only corporations benefit when clean air is a luxury.