Make Your Own Air Purifier For 200 RMB? Really? Really.

DIY air purifier filter PM2.5 china
Kids, DO try this at home!

Last January we had the airpocalypse, and this January — hell hath frozen over. Because a bright-eyed Fulbright scholar and his disciples are spreading across China, preaching in their revival tents to swooning crowds that “you — yes, YOU, ma’am, in the corner!” (rising applause) “Yes, I swear to you right now that you can make your own air purifier for under 200 RMB — and get the same results as your fancy-schmancy, Perrier-sipping import! Can I hear a yee-haw!” (wild clapping).

I refer to Thomas Talhelm’s evangelistic, data-filled blog and his company spinoff, Smart Air Filters, offering frequent DIY workshops on just this subject, as well as selling their own two models. And yes, the cheaper one is really only 200 RMB. Crazy, no? Like a fox, maybe. Because Thomas’ scrupulous data, far geekier than anything I’ve written (that’s a compliment), does indeed show quite impressive PM2.5 reduction with these machines, even when directly compared to some famous models we all know about.

Thomas actually was inspired to do his own testing from all of my own tests and blog posts, and we’ve been emailing back and forth since last summer, comparing notes. As I mentioned last week in my Philips review, I’m quite a fan of his goal to find affordable protection for the masses against indoor air pollution. And his message has spread quickly, with many news groups covering the story. Many of my readers have asked me to review his machines, and I recently got to test both his Original and Cannon. So how did they do? Is he a prophet or a charlatan?

Let’s cut to the chase: a true HEPA filter and a strong fan indeed are all you need to eliminate bad particles in the air. Almost every top air purifier machine out there, no matter how fancy, is still built around those two pieces: a HEPA filter rated to eliminate 99% of particles larger than PM0.3, and a fan blowing air through it at a proper flow rate. No other features really matter as much as this, at least here in China. If you have a car, a HEPA filter can go into your exhaust system and clean your air; if your home or office has an HVAC system, installing a top-rated HEPA filter is incredibly effective, and much cheaper than a floor machine.

So yes, it makes perfect sense that a do-it-yourself combo could work — and it does. I tested the smaller Original model in my three small rooms, 10-13 square meters in size, overnight with the doors closed. And this little guy did about as well as any other machine I’ve tested: PM1 levels were 91% lower than the outdoor air, and PM5 levels were 95% better. This was on its lowest speed setting, which was tolerably loud but certainly noisier than my usual Blueair settings at night. In my most recent testing of Blueair, IQAir and Airgle, I got bedroom results of 88-90%. For small rooms, this little HEPA filter was at least as efficient as all of the big boys.

Thomas tests his machines a bit differently than I do, comparing them to the same room before and after, and he also measures PM0.5 and 2.5, whereas my Dylos machine measures PM1 and 5. He also mostly tests on highest fan speed, which I find impractical and too noisy for a real world scenario. But even with these differences, we still got about the same results: effectiveness always at least in the high 80%, which also at the very least was a strong match to the bigger machines — sometimes better.

So our data does match, and again why wouldn’t it? He’s using a real HEPA filter and a fan with a flow rate that works. I think their smaller Original model is especially a reasonable option for students and people with limited income to use in their bedrooms. It certainly is far, far better than having nothing at all, when the AQI outside is crazy bad.

DIY air purifier Blueair Philips Thomas Talhelm PM2.5His newer machine, the 450 RMB Cannon, was designed for bigger rooms, and I think that also could work well in theory, since it’s the same HEPA filter on a stronger fan. I wish I could share hard data with you, but honestly I didn’t get a lot of data points on this machine, mostly because it was just so darn noisy that I didn’t want to test it any more in my living room. Even at the lowest setting overnight, it was much louder than normal background decibels from my current IQAirs. For me at least, that’s a non-starter as an option. Thomas openly admits that the Cannon is a bit loud, but it still is effective even on low settings (see the graphic to the right).

But let’s not get bogged down in the details of these two models. These are early, first generation attempts, and besides, it’s distracting from his and my main message: everyone everywhere should always try to limit their exposure to pollution, and a DIY HEPA filter and fan combo are a heck of a lot better than nothing at all.

I assume the PR teams at the famous air purifier headquarters are now champing at the bit to correct me, aghast that I would gloss over their superior technology. And of course that’s partly true, as some top end filters do indeed claim to filter down to PM0.003, a hundred times smaller than a normal HEPA. Not to mention the other filters for VOCs and other chemicals besides PM. And maybe that does matter in a place as polluted as China — but I haven’t seen any data or medical resource claiming any specific advantage in targeting those ultrafine particles. Perhaps in the next couple years, with better research, we may learn that spending that extra $$ on the top end models may prove more beneficial to your health.

Until then, I say to the hundreds of thousands of people who’ve bought air purifiers: keep up the good work. But for the hundreds of millions of unprotected people across the developing world, anxiously awaiting the next inevitable airpocalypse — go get a HEPA filter and stick it to a fan. And buy yourself a particle monitor, test your machine, and blog about it. Viva la consumer revolution!

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26 thoughts on “Make Your Own Air Purifier For 200 RMB? Really? Really.”

  1. Great post. Thanks for the tips. If not solely for the economic relief this alternative system presents, it offers an amazing opportunity for students and families to get more involved in our collective health.

    I would love to hear more and get in contact as the educational program we are starting at ISB seeks to get students involved with projects just like these! Please let me know how we can get involved. The small “project- based” school will start in the Fall of 2014.


    1. Hi Kyle. Thanks for the kind words, and I’d love to help with your school’s science project! I think a lot of kids would be really interested in testing out different machines, HEPA filters — even comparing them to their big machines at home. You’ll need a good particle monitor but lots of schools around here already have these. Sure, let’s chat some more about this! I’ve done a lot of talks at ISB and it’s always an honor and fun to work with the students.

  2. Hi Y’all

    I have built one purifier a long time ago. It is really not any rocket sciences but as stated also above, the noise is a challenge. Building one is kind of useless without a monitor.
    I like to ask about Dylos monitor. I found their web pages. Which model Doctor is using and can Dylos monitors be bought in Beijing?


    1. I use the cheaper Dylos 1100, not the Pro 1100. It was $200 USD on, and it measures PM1 and PM5. The Pro measures PM0.5 and PM2.5. You can also get on Amazon China but it costs a lot more…

      1. Hello doctor,

        How do you manage with the voltage problem to charge the Dylos u bought from USA? The product says it supports only 110 volts

  3. This is very interesting. I should try it for my kitchen and other indoor area that hasn’t a filter yet.

    Btw, where can you buy a HEPA filter? From the same supplier that we buy our air filter machine from?

    Thank you vey much.

    1. Hardware stores should carry HEPA filters, but maybe it’s easiest online! Tmall, Amazon China, Jingdong, all carry HEPA filters. I would stick with famous brands, especially 3M but there are plenty of others.

  4. I’m biased here, but I thought that was a good, balanced review. The cannon kicks butt, but it is too noisy for some, so I recommend looking at the decibel readings before making a decision:

    The Original is quieter, but for people who are very sensitive to noise, I think the Philips AC4072 model is a good choice, and it’s done very well in my tests.

    And I think you’re right that we’re in the early innings. There’s a lot of progress to be made! For example, I was fortunate to have an expert in acoustics volunteer to go over our design, and we are now testing a new model that may be able to retain the power of the cannon with much lower noise. I’ll post those results when I get them!

  5. Doctor

    I bought one for the office and works well. My only question is how often should the filters be replace?



  6. Essential read(s)! Thank you! ‘Spammed’ everyone with this

    Mask and home air purifiers in place, what is there to do for an open office space? think 300 sq meters of cubicles and small individual offices.

    Hepas in the air vents? there are about 15-20 of them and the filters must be changed every 3 months at least [or so I hear]. My [all Chinese] superiors and workmates are hard to persuade

    What is the average air quality in office buildings with the usual AC systems?

  7. We have been using the DIY ones from Thomas in our Chengdu apartment since last fall. I find they have made a big difference. We are only here on a one year sabbatical and investing in other machines just didn’t make sense. Not soon after arriving, however, there was lots of hacking from several of us until I found the Particle Counting tumblr and bought a few fan and filter combos. I figure even if they are far from perfect, they have made great improvements in the air and help us recover from the rest of the time when we are out and about.

    We have been changing filters every 6 weeks or so, as they are really gunked up by them. One runs almost 24 hours (moving from bedroom to living room and back). The other two probably 12 hours a day when the kids are home and bedroom doors are open.

  8. Thank you for your cool post but you left a key item. People must buy HEPA 12 or HEPA 13 filter to achieve 99% effeciency or to catch the smoke particles. I am spreading this from other youtube videos in the neighboring country he he.

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  10. Hi Dr. Saint Cyr, I’ve read most of your “clean air” posts. Thanks so much for the helpful information. My wife and I are now considering buying air purifiers for our home. I also read more on the Smart Air website.

    Since you mention that the “cannon” is quite loud, I had considered buying one and running it at night in our living room while we slept so the noise wouldn’t affect us like it would during the day. My rationale was that it could clean the air at night (much like you might set your dishwasher to wash dishes at night while you are sleeping, then wake in the morning to clean dishes!).

    But based on a few of the charts/graphs that they post, it seems that, after filters/fans are turned off, the particulates in the air seem to increase dramatically. So would this render the night-use of air purifiers in the living room ineffective?

    A dehumidifier needs to be run often to keep moisture levels under control. But with an air purifier, once it cleans the air well, shouldn’t the air stay reasonably clean (unless there was a lot of in and out traffic in your house/room)?

    1. Hi Graham, I wouldn’t recommend shutting these off/on regularly and would keep on 24/7. There is quite quick diffusion and air coming in from the outside, in most houses and apartments.

  11. This is incredible! Thanks so much. I definitely want to try this out.

    Relatedly I have a question. I posted your article and the Taobao store on FB. An engineer friend of mine suggested that “because HEPA filters are usually made of glass fiber, you have to be careful that maybe that doesn’t start getting blown out. They’d act like asbestos.” He thought sitting it well so it stays put was the key.

    I checked briefly online and was not able to see anything easy to understand to the lay person’s mind. Do those air purifiers with multiple filters have a function to protect against HEPA filters falling apart, and is that a necessary thing? Would changing it regularly take care of glass fiber in my room??

    I would love to hear if Thomas Talhelm has an opinion on that. Thanks further!

    1. I’ve never heard that they’re basically made of glass fiber, nor have anyone I’ve chatted with. I’m not sure what they’re made of, actually, but I’ve never heard of even a potential issue with the filters themselves being a potential problem. Perhaps someone else can chime in here?

      1. Gus Tate from Smart Air got back to me! Very excited to try one this season. Thanks always.


        Hi Michiko, thanks for reaching out. Our filters are made of plastic fibers and not easily damaged. I wouldn’t go cutting it up intentionally but it is fine to handle with your hands.


  12. Not sure where the best place to post this question:

    Keeping in mind that all air pollution is bad…

    Is a AQI 250 day twice as bad as a 125 day, or is it exponentially worse?

    Thanks for your work; I’ve passed on some of your articles to friends and colleagues in Shanghai and they have found it quite informative.

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