Can DIY air purifiers clean large rooms? Hundreds of hours of Smart Air tests have found that DIY air purifiers cut fine particulate, reduce smoke, remain effective over 200 days, and even capture chemicals like formaldehyde. But an important practical question is whether DIY purifiers are effective enough to purify large rooms.

DIY Air Purifier Search

To answer this question, I tested every fan I could find, as long as it had a flat front. I was looking for a fan that put out a lot of air.

After getting all the data, of one fan stood out above the rest. I called it “the Cannon.”

In Anna’s 15m2 Beijing bedroom, it crushed particulates. It removed 97% of the small .5 microns particles.

But how well can it do in larger rooms? Most companies estimate this using flow rate, but those calculations depend on how well houses are sealed and how dirty the air outside is. I wanted to know how well a DIY air purifier can clean under real-world conditions.

DIY Air Purifiers Clean Large Rooms: The Test

I tested the Cannon on its high setting six times in a 30.5m2 living room–a large, open space. To track pollution, I measured 0.5 and 2.5 micron particles using a Dylos laser particle counter. Each test lasted at least three hours.

I calculated the percentage reduction in particles from the first hour to the last hour.

Besides testing in a big space, this experiment extends the findings of the earlier room tests because:

1. These tests were run in the daytime. Several people have the intuition that pollution goes down at night because people are less active and fewer cars are on the road (but the data shows that intuition is false–PM2.5 pollution is worst in the middle of the night in Beijing).

2. These tests were run while people were moving around in the room and opening the door to the outside. This is more conservative than the nighttime tests because the Cannon has to fight influxes of outdoor air.

DIY Air Purifiers Clean Large Rooms Effectively

Over six tests, the Cannon removed 92% of .5 micron particles and 89% of 2.5 micron particles even with people moving around and opening doors.

In previous tests, 2.5 micron reductions were usually slightly larger than .5 micron reductions, so it’s a little surprising that the 2.5 micron reduction was 3% lower than the .5 micron reduction. My guess is that this is because people were moving in the room, and human movement affects the 2.5 micron readings much more than the .5 micron readings.

As always, I’m posting the raw data and more details on the methods for fellow nerds below.

Raw data