How to Get the Most Out of Your Purifier

If buying an air purifier is the first step to breathing clean air, the second step is knowing how to use it best! Here are the 4 most important things to know about how to use an air purifier—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.


the HEPA remained effective long after it had turned black

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.


check the hepa lifespan in order to get the most out of purifier

note down the date of purchase to get the most out of purifier

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.

keep the room well-sealed to get the most out of purifier


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.


particles in room: windows opened vs. window closed


3. Where to Place Your Purifier

Many people place their purifiers against the wall because it’s out of the way and looks nice.

placing your purifier against the wall does not get the most out of it


But how does that affect the purifier’s performance?

For purifiers to work best, they need room to take in the air and push it out to the room. If it’s backed up against the wall, it can’t take in as much air.placing purifier against the wall does not get the most out of it

Just how far from the wall does it need to be? I decided to put our purifiers to the test.


The Test Method

Test the distance of the purifier and the wall to get the most out of the purifier measure the airflow coming out of the purifier

I ran the test on the Blast, Blast Mini, and Cannon. When the purifier was flat against the wall, the airflow was only about 5%! When the purifier was 4cm from the wall, the airflow increased to 94%. At 10cm (the length of a typical computer mouse) from the wall, airflow was back up to 100%.


distance against airflow

Bottom Line

For maximum performance, you should place your purifier at least 10 cm away from the wall. However, even just 4 cm away from the wall (about the length of a pen cap) will give close to top performance.

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.

when should I run my air purifier

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.

how long does it take for the room to get dirty again

The data showed that particulate levels returned to 50% of baseline the pollution level 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.)

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i hv hitachi epa 6000 which blows out clean air from top. it sucks from side gaps left and right. i placed the air purifier on the shelf. there is a gap of 20 cm from top of the air blower inbetween the ceiling. is that ok?

Liz - Smart Air

Hi Alex, we’ve never tested the model you are using. I think the best way is to spare it as much space as possible both for air inlet and air outlet. If you don’t have enough space for it, the best way to tell the threshold, if you have a budget, is to get an air quality monitor and see how well it works.


Does the hight placement of the filter have any effect on purification? Am I correct in thinking that there is more pollution closer to the ground, or does the action of the fan change all this if using, for example, the Squair in a 20m2 room?

Liz - Smart Air

Hi Simon, good question! In fact the air quality within a room, closer to the ground or the ceiling, doesn’t have a difference. Even living in a high rise building wouldn’t not make an obvious difference of the air quality: All of the tests we did are real room test in a Beijing apartment. So if the air monitor shows clean, it means the whole space is cleaned. For example, using a Sqair in a 20 sqm room, you will see the air quality monitor shows the same PM2.5 number close to the air purifier or farther away across… Read more »


Hi – i see that i can easily clean the Blast and Blast mini when the cover is taken off but may i ask if i should clean the Blast mini air inlet and also where the fan blades are? will that require cleaning and is it easy to do so?

Hey Angie! The pre-filter for the Blast and Blast Mini is on the back. It’s the black, mesh-like filter. This can be removed and washed with water and then left to dry. We recommend you do this every 2-4 weeks depending on how often you use your purifier! You can find more information in the Blast and Blast Mini manuals.


When to change air filter must be depending on particle mass/ volume air and amount of air pressed thru the filter. 1. I run my filter during a relatively clean period on max for 1 h , thereafter on min rest of the night. 2. I run my filter during heavy polluted times on max for 2 h, thereafter on medium rest of the night to handle the outside air seeping in. The filter load is obviously not the same and to set a lifespan of 140 hrs is, in my mind, not correct. My intention is to use a… Read more »