I’m on a quest to make a DIY air purifier. Step one was my research into how different filters work. Based on that, I concluded that a HEPA filter is all you really need to make an effective air purifier and fight particulate air pollution somewhere like China or India. Given the fact fancy air purifiers run for 8,000 RMB in Beijing, or 100,000 INR in Delhi and most people don’t have that kind of money, I thought I’d try making my own DIY air purifier.
Wait, Does the DIY Purifier Actually Work?
I’ve tested the heck out of this DIY air purifier! The data shows it works, even for tiny PM2.5 particles, compared to the big brands, with a control test room, over 200 days, and in a completely controlled test environment). But here I’ll explain how I made it.
How to Make a DIY Purifier
#1 Buy a fan
It’s important that it has a flat front or back 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):
#2 Buy a HEPA filter
For my very first homemade air filter, I first bought this one for 108 RMB (US$16):
Since then, I tested HEPAs from all the manufacturers I could find to see if I could make an even more effective DIY air filter, and found one that captures more particles and has better air flow. Because I buy it in bulk and ship it through the shop for my social enterprise, it costs less (75 RMB) than that first HEPA I bought. I’ve tested this HEPA filter with my particle counter, so I know it works (watch live DIY filter test here).
#3 Pull the grating off the front of the fan
This is where the DIY fun starts! It helps if you have pliers for this. Then turn the power setting to 3 and pull the knob off – we’ll be using this DIY air purifier on the highest setting.
The knob gets in the way of the HEPA. Without the knob, I turn my DIY air purifier on and off by plugging and unplugging it.
#4 Strap on the HEPA
Use string to strap the HEPA filter onto the front of the fan, and you’re done! Your very own DIY homemade air 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, make yourself a fancier DIY air purifier by finding a fan without a metal bar in the front, like the DIY air purifier I ship through Smart Air.
#5 Admire your new DIY air purifier
Total cost for this DIY air filter: 166 RMB (US$27). Compare that to 8,000 RMB ($1,300) for the fancy purifiers here in Beijing. I now ship a simple fan and a filter with a simple upgrade that increases clean air output by 15% over my original design for 228RMB (US$37).
Your next question is probably, does this DIY air filter work? See a live test here. Here are a few other important questions:
- Filters: What combination of filters do I need to protect against everything?
- Stronger fan: Tests with the DIY Cannon
- How can I test it: Comparison tests of common air quality monitors
P.S. Should the filter go on the back??
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 put it to the test, and the results surprised me.
Thomas is an Associate Professor of Behavior Science at the University of Chicago Booth School of Business and the founder of, a social enterprise to help people in China breathe clean air without shelling out thousands of dollars for expensive purifiers.