Several people have asked me if they can use a purifier in the living room to clean their entire apartment. The benefit is that it’s easier to use just one purifier. Plus, noise isn’t an issue if the purifier is in the other room. But does it actually clean the air in the entire apartment? Even if the bedroom door is closed?

The Full Apartment Air Purifier Test

I tested this in a large 134m2 (1,442ft2) Beijing apartment by putting the Blast purifier on a timer to turn on high every day from 7pm to 7am. A Laser Egg air quality monitor in each room kept track of PM2.5 continuously (how accurate is the Laser Egg?).

The Blast is a strong purifier. It puts out 890 cubic meters of clean air per hour—that’s equivalent to running three and a half BlueAir 203’s on high.

One bedroom door was always open; one was always closed. I switched which room was open and which was closed for half the tests. Windows were always closed.

Air Purifier Test Results

Over 9 tests, the Blast reduced PM2.5 in both the room with the door open and the room with the door closed. However, the room with the door open (the Open Room) had 18% larger reductions.

That makes sense, since the purified air coming out of the air purifier could more easily enter the open room.

However, keeping the bedroom door open kept open also had its downsides. At the start of the test, the room with the door open had higher PM2.5 levels than the closed room.

In this case, the open door was letting in more dirty air from outside.

Although the room with the door open got more of the clean air from the air purifier, this room was dirtier at the start of the test. At the end of the test, both rooms had similar levels of PM2.5.

The Dirty Air Bounceback

In the two hours after the test ended, PM2.5 bounced back faster in the open room.

Open rooms have more air flow, which allows in more outdoor PM2.5. This quick bounceback is consistent with our earlier tests, which found that outdoor air pollution enters our homes constantly and quickly. That’s why I don’t recommend running the purifier for a bit, then turning it off.


These test were performed in a single-floor apartment, in two setups. One setup with the Blast air purifier in the hallway, and one setup with the Blast in the living room. In the living room setup, the air purifier was a long way from the two bedrooms (around 10-12m/30-35ft away). Despite this, the Blast was still able to clean both bedrooms fairly well.

We have not performed tests for houses or apartment with multiple floors. However if the air purifier is strong enough it’s reasonable to assume that an air purifier downstairs may be able to help a little in cleaning the air in upstairs rooms.

Bottom Line:

  • The Blast was able to reduce PM2.5, even when it was outside of the bedrooms, even through a closed door.
  • Reductions were 18% larger in the open room.
  • Tests with the purifier inside the room find larger reductions.

Open Data

As always, I’m making the data openly available for all. You can download the day-by-day statistics here (Part 1, Part 2). For the full (totally overwhelming) minute-by-minute data, email us at [email protected].

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