How to Make a DIY Air Purifier

Based on my research into how different filters work, I concluded that a HEPA filter is all you really need to fight particulate air pollution in China. Given the fact fancy air purifiers run for 8,000 RMB here in Beijing, and I’m only here for a year, I thought I’d try making my own DIY purifier.
I give data on how well it works here (1, 2, 3, 4), but here I’ll explain how I made it:

  1. Buy a fan. It’s important that it has a flat front so that you can strap the HEPA filter to it.
    Fans with flat fronts usually have a recessed motor unit, so look for that. Here’s the one I bought for 58 RMB (about US$8.50):

1

  1. Buy a HEPA filter. I first bought this one for 108 RMB…

2

But since then I tested HEPAs from all the manufacturers I could find, and I found one that captures more particles and has better air flow. And because I buy it in bulk and ship it from my Taobao site (also smartairfilters.com), it actually costs less (75 RMB) than that first HEPA I bought. I’ve tested it with my particle counter, so I know it works.

  1. Pull the grating off the front of the fan. It helps if you have pliers for this. Then turn the power setting to 3 and pull the knob off.

The knob gets in the way of the HEPA. Without the knob, I turn the fan on and off by plugging and unplugging it.

3

  1. Use string to strap the HEPA filter onto the front of the fan, and you’re done! Your very own DIY purifier.

The metal bar in the middle will stick through the filter a little bit. You could saw the metal bar off, but my tests show it doesn’t seem to make a difference. Or better yet, find a fan without a metal bar in the front, like the type I ship now (Taobao).

4

5

Total cost for this DIY purifier: 166 RMB (US$27). Compare that to 8,000 RMB ($1,300) for the fancy purifiers here in Beijing. Your next question is probably, does it work? See a live test here, how well it works if we use a stronger fan like on the DIY Cannon, or comparison tests with the big brands.

And you might be wondering, “shouldn’t the HEPA go on the back of the fan?” I always thought the answer would be “it works just as well both ways,” but I tested it, and the results surprised me.

P.S. Thanks to Artur Weber for translating the instructions for air-breathers in Portuguese-speaking countries!

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