## How Big of a Room Can the Cannon Clean?

After I tested every fan in China I could find with a flat front…

…the results of one fan stood out above the rest. Because of its appearance and how much butt it kicked, 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. Since air outside is dirtier in China, I think it’s necessary to do real-world tests.

Methods

Fortunately, I moved into a large 4-bedroom apartment, with a 30.5m2 living room. I tested the Cannon six times on high and tracked particulates with a Dylos particle counter. Each test lasted at least three hours.

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

This test also serves as an important extension 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–PM 2.5 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.

Results

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.

Conclusion

The Cannon can clean rooms at least 30.5 m2, which puts it above the 22.3 m2 Blue Air recommends for their 3,6000 RMB 203 model.

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

## Independent Tests

Beijing-based Dr. Saint Cyr’s tests of air purifiers were one of my original inspirations for the whole DIY project, so I was happy to see that the DIY recently became a part of those tests:

These are the first independent tests of the DIY, and the results parallel mine. You could also include the tests by doctors at the University of Michigan as independent  “proof of principle,” although they used a different fan and filter. The commonality is that all of the tests have shown that a simple filter and a fan can reduce particulate pollution in the home.

Dr. Saint Cyr’s review isn’t all glowing. He rightly notes that the cannon is noisy, which I’ve also written about (decibel counts and comparisons here). Tests show the cannon is still very effective on the lower settings, so I recommend running the cannon on the somewhat quieter settings. And for people who are sensitive to noise, I recommend the quieter Original.

Saint Cyr writes that we’re still in the early rounds of our design, and I think that’s right. In fact, we’re working on a new model that keeps the high performance with less noise. I’ll be posting more data on that in the coming months.