Harder, Better, Faster, Stronger DIY

Ever since I started my DIY experiments, I’ve been wondering whether I could create a super DIY by using a stronger fan. In the past three months, my collaborator Anna has helped me test a half dozen different fans. She now has a home full of fans:


After months of tests, one fan has proven itself to be the king of fans. I’m now ready to unveil a newer, more powerful DIY:

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Informally I’ve been calling it the “大炮,” the cannon. That describes how it looks, but also what it does to air pollution. Simply put, this thing kicks butt:


Even when you look at the really small stuff–0.5 micron particles–the cannon is equally impressive:


Over five nights of testing, the cannon removed an average of 97% of 0.5 micron particles and 96% of 2.5 micron particles. I think this may be close to the upper limit of how much particulate pollution you can remove from your air with a home-use filter.

(Update: for more Cannon room tests, check out tests with an added carbon layer and tests on the medium and low settings.)


But wait, isn’t the original DIY effective too? That leads to the question…

What’s the difference between the Original DIY and the Cannon?

  1. In 8-hour tests, the cannon removes 4-13% more particulates. 

In the overnight tests, the cannon is removing somewhat more particulates–especially the smaller 0.5 micron particles.


Remember, this is an average, so the difference is larger on very polluted days and smaller on clean days. (You can see the data for individual days in the raw data at the end of this post.)

  1. The Cannon cleans faster.

Because the cannon circulates air a lot faster, it reaches those numbers faster than the original DIY.

This is harder to illustrate than average effectiveness, but you can see it clearly in our controlled tests. In the controlled tests, we burn a source of 0.5 micron particles (a stick of incense) in a small closed room. After 20 minutes, we turn on the filter. In those tests, the Cannon is clearly faster:


Now, this speed test is only to demonstrate relative speed in controlled conditions. The speed test room was small–a bathroom. It’s not meant to say the Cannon will clean your whole bedroom in 1 minute. But it does say the Cannon will clean your room faster than the Original DIY.

  1. The Cannon is better suited for very large rooms.

Some people have told me they want to use the original DIY to clean large spaces, like stores and multi-person offices, but the original DIY is not really made for large spaces. If you want to clean a large area, the Cannon has the power to get the job done. (See tests in a 30.5 m2 room.)

Is it still affordable?

One obvious question is, sure it works better, but won’t it be way more expensive? The stronger fan is more expensive and heavier, but we’ve still managed to get the price at Smart Air to 450 RMB. At that rate, you’d be removing 97% of your 0.5 micron particulate at just 4.1% the price of the 11,000 RMB IQ Air.

When should I choose the Cannon vs. the Original DIY? 

I would recommend the Cannon for:

  1. People with larger spaces, like large offices or bigger-than-normal living rooms.
  2. People who are very concerned about air pollution and therefore really value that extra speed and effectiveness–for example, people with health problems, pregnant women, and children.

But for most normal-sized bedrooms (<15m2), the Original DIY will still do the trick.

As always, I’m posting the original data and methods below for fellow data nerds.


The Limits to Counting Particles

If Particle Counting has just one take-home message, it is that you can protect your yourself from particulate pollution in China, and it costs a lot less than filter companies want you to think. However, I don’t want to mislead people into thinking that turning on a filter will definitely solve any possible problem. I talked with Louie Cheng, who founded Pure Living China, a company that tests for pollutants in homes and offices, and we came to a few conclusions about the limits of filters:

  1. Particulates are not everything. 

Particulate pollution is a big deal in China, and it’s bad for your health. There are lots of studies out there showing this, but the one that pops into my head the most is the study showing babies exposed to more air pollution are born with smaller heads. If that’s not scary, I don’t know what is.

However, particulates are not everything. Gas pollutants can be a problem too. Although I suspect that almost every home in China has particulate pollution while only some have gas pollution, there are dangerous gases out there like radon, carbon monoxide, and the broad category of “volatile organic compounds.” Unfortunately, even the fancy filters have trouble consistently capturing a wide range of gases.

If you’re considered about gases, consider getting a home test from Pure Living China. They’re not cheap, but I’d consider it if I had unexplained health problems or a child at home.

I try to write “particulate pollution” rather than “pollution” because not all pollutants are particulates. However, it’s easy to just covert “particulate pollution” to “pollution” in our minds.

  1. Some particles are too small for filters.

A quick look at the size of different particles and gases makes it clear that particulate filters can’t get everything:


HEPAs are rated to .3 microns (micrometers), and I’ve seen reports that they can get particles of .1 microns, but there are still leftovers. For example viruses and gases will pass through air filters (but not bacteria). (This, by the way, explains what I call “the smoker paradox.” More on that later.)

  1. Opening your window is good (sometimes). 

The air outside in China is scary, but sometimes it is actually good to open your windows. That is because some pollutants can come from inside. Some common sources are formaldehyde used in some furniture, cooking without a good vent, and construction work.

In those cases, it can actually be a good thing to open your window, particularly on blue sky days.

Conclusion: Air purifiers will get a lot of pollutants out of your air, but there are limits to what you can filter out. Consider opening your windows on clean days–and particularly if you have renovation going on indoors or are cooking without an adequate vent.

Thank you to Louie Cheng for sharing his expertise.