The Original

For 200 RMB, we'll send you a fan, HEPA filter, and a strap. Assemble it just like we did or choose a pre-assembled unit. Either way, shipping's included.

Order a kit »


The Cannon

Stronger fan, lower particle counts, faster results. If you're looking to clean a larger area, check out the new beast.

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HEPA filters

HEPA filters are what trap small particles like PM 2.5, and they're not expensive! We buy ours straight from the factory so we can pass the savings on to you.



We think if most people knew how air filtration works, they'd think twice about paying thousands of RMB for a fancy machine. Check out Thomas's Particle Counting blog, attend a workshop, or just keep reading.

See the data »

DIY kits: Now with two fan options:


The Original

The Cannon


Original Cannon


(average percent reductions, based on 8-hour tests in a 15 sq. m. bedroom)

Original Cannon


(based on a 1-hour test in a 1 sq. m. bathroom with a source of PM.5 pollution. Get the full story here.)

Original Cannon


200 RMB

450 RMB

Our advice

Suitable for normal-sized rooms.
Quieter than the Cannon.

Suitable for larger spaces
and anyone wanting clean air fast.

More info

Check out Particle Counting for more details.

Order delivery. Or takeout.

Original kit: 200RMB


1 fan, 1 filter, and 1 strap.

200RMB or $33 USD.


(Order more by changing the quantity on the next page.)

Cannon kit: 450RMB


1 fan, 1 filter, and 1 strap.

450RMB or $75 USD.


(Order more by changing the quantity on the next page.)

Extra filter: 80RMB/90RMB


1 HEPA filter (choose Original or Cannon option).

80RMB/90RMB or $14/$16 USD.


(Order more by changing the quantity on the next page.)

Extra prefilter: 10RMB


1 pre-filter.

10RMB or $2 USD.

Must be shipped with other items.

(Order more by changing the quantity on the next page.)

Extra strap: 10RMB/12RMB


1 velcro strap.

10RMB/12RMB or $2/$3 USD.

Must be shipped with other items.


(Order more by changing the quantity on the next page.)

Don't forget to enter your shipping address in Chinese and your phone number in the special information field!

We offer free shipping within Mainland China. We can also ship to other countries serviced by SFExpress for customers willing to pay for shipping via cash-on-delivery. Check SFExpress for availability.

Having trouble with PayPal? Visit our Taobao store for more China-friendly payment options.


Live in Beijing?

Smart Air Original DIY kits are now available for purchase at Natooke! Located on Wudaoying Hutong near Yonghegong subway station. Cannon DIY kits are only available online.


We run workshops to let people know it doesn't cost thousands of RMB to get clean air. Participants make filters to take home, and we test them on the spot with a particle counter.

Next workshop:

Culture Yard, Beijing

Clean air is coming to Culture Yard in Beijing! 250 RMB covers the cost of the filter parts plus free flow tea, coffee, and soft drinks from Culture Yard.

Date: Sunday, August 24, 1:00pm

Location: Culture Yard

Cost: 250 RMB

RSVP here

Culture Yard
No. 10 Shique Hutong
Dongcheng District

(Line 5 Beixinqiao station, exit C and walk 400 metres to your left)

Want to host a workshop at your school or office?

Let us know what you need at least two weeks in advance, and we'll start planning:

Keep abreast.

Sign up for our mailing list to hear about future workshops and new filters.

Wechat QR Code

Scan here to follow Smart Air on WeChat

Let's break down the question of how well a DIY air purifier works into three smaller questions:

  1. Is the air coming out of the purifier clean?
  2. Is the air coming out of the filter enough to actually clean air in the entire room?
  3. How well does it perform compared to expensive purifiers?

1. Is the air coming out of the purifier clean?

This is the easiest question to answer, and we do it by holding the particle counter in front of the unit and watching the numbers drop. Here's a Youtube video of Thomas doing just that (for a video that is easier to access in China, see Thomas's post on Particle Counting):

Conclusion: Yes, air coming out of the purifier is clean.

2. Is the air coming out of the filter enough to actually clean air in the entire room?

Answering this question is more difficult because you need a controlled environment (for example, you don’t want to walk in and out of the room during the test), and you need to test the air for a longer period of time. But fortunately for you, Thomas is a huge nerd and does this kind of thing for fun.

To answer this, Thomas set up the particle counter on one side of his 13.5 m2 bedroom and put the DIY filter on the opposite side of the room. Here's what our filter did in one hour:


And over the course of eight hours:


The particle counter also gives data on PM .5 — even smaller than the PM 2.5 reading. Here's what that looks like over eight hours:


Conclusion: Yes, the clean air from the DIY filter is cleaning the entire room.

For fellow nerds, here are some more details on how the tests were conducted:

The test above was done starting at 11:30pm on 6/16/2013, when the outside AQI in Beijing was 230 according to the US embassy's AQI Twitter feed. (The outside air improved the next day, but results were similar on a later test where AQI actually went up slightly from 195 to 202 during the test.)

According to comparisons of our particle counter's tests of outside to US embassy AQIs, an AQI of 230 would convert to about 2,650 on the PM 2.5 count on the reader. (Remember, the particle counter gives the raw number of particles 2.5 micrometers and above per .01 cubic feet. The US embassy takes mg/m3 and converts that to an AQI. Therefore, the raw numbers are different, but they correlate highly. You can think of this as the difference between measuring attendance at a basketball game by the number of people in the stadium versus the total weight of those people. The two numbers are highly correlated, but not identical.)

Thomas did the test in his bedroom with the doors and windows closed. The room is 13.5 meters squared, with two windows.

The particle counter tends to take a 5-10 minutes to get stable readings, so to be conservative, Thomas gave it about an hour:


The spike at the top was when Thomas entered the room to turn the air purifier on and reset the machine, so it may be the dust he kicked up by walking around. A more stable reading for that time would probably be about 230.

The uptrend prior to turning the filter on may have been because Thomas was running a dehumidifier (which itself has some small filters) in the room before the tests.

Regardless, this data suggests that the effect of the filter was not a confound of calibration.

3. How well does it perform compared to expensive purifiers?

Thanks to two kind souls who donated a Blue Air 203/270E (3,600 RMB) and a Philips AC4072 (3,000 RMB), we've finally been able to test the DIY against expensive brands in the same room, for the same amount of time, with the same particle counter.

To do that, Anna ran 11 overnight tests with the Blue Air and 9 tests with the Philips. As always, Thomas calculated effectiveness as percent reduction in particulates from the room air. Anna tested the air before she turned on the air filter, and then set the particle counter to take hourly measurements of the air in her 15 m2 room. Anna used the highest setting on each filter. (See the end for the full methodology.)

And here are the results:


The cannon came out on top. It removed more particles .5 and above than any other filter, and it tied the Philips and Blue Air on particles 2.5 microns and above. Not bad for 450 RMB!

Yet all four filters were making the room air significantly cleaner. For particles 2.5 microns and above, all four removed over 90%. For particles .5 microns and bigger, all four removed over 80%.

Based on the data, here’s how much you’re paying for each percentage of PM .5 reduction:


Recently, a Chinese news article claimed air filter companies are making “falsely inflated profits.” That fits with this data showing that the cannon removes more particulates than the Blue Air, yet costs 1/10th per percentage of PM .5 reduction. Similarly, the original DIY removes 4% less PM 2.5 and 6% less PM .5 than the Blue Air on average, yet the Blue Air costs more than 16 times as much.

Conclusion: You can remove particulate pollution from the air in your home and pay far less than a Blue Air or Philips.

Granted, particulates are not everything. There are also gases like radon and carbon monoxide. People who suspect that their homes may have harmful gases (particularly people whose homes are being remodeled) can get home tests done for gases from HEPAChina. It’s not cheap, but I’d consider it if I had a baby at home.

For fellow nerds, here are more details on our data and methods:

Machines: The Original DIY and the Cannon are the units we ship from Smart Air. The Blue Air was the 270E model. The Philips was the AC4072.

Calculating effectiveness: As always (1,2), to calculate effectiveness, I average the particle counts for the last four hours and divide that by the baseline number. As I’ve said before, I think this method of calculating effectiveness is more rigorous than calculating the reduction versus outside because indoor air is cleaner than outdoor air.

Sample timing: Anna took the baseline measurement before she went to bed. Then she set the particle counter to take hourly measurements until she woke up in the morning.

Room setup: The DIY filter was on one side of the room. The particle counter was on the opposite side. Anna made this schematic of the experimental setup:


Anna’s room is 15 meters squared. The windows were closed at all times, and the bedroom door was mostly closed before Anna went to bed, and it was always closed during sleeping hours.

Particle Counter: Our particle counter gives counts for (a) particles .5 microns and above and (b) particle 2.5 microns and above. For more information on how laser particle counts compare to government machines and AQIs, check out Thomas's data comparing the two over 70 measurement occasions. (Spoiler: they correlate at r = .89.)

Filter Life: The owner of the Philips estimated it had been used previously for a few weeks. The owner of the Blue Air estimated the current filters had been used for approximately 6 months, which means it was about time to replace the filters.

(Most people overestimate how much the newness of filters matters, except for with very old filters. For example, the Blue Air was still doing an excellent job at 6 months. Keep in mind that, over time, HEPAs actually become better at catching particles because particles “fill up” the spaces in the filter. The downside is that air flow decreases. However, if anyone has a Blue Air with new filters, contact us and we’ll run the tests!)

Interpreting the speed of the drop: The time between (1) turning the filter on and (2) the nearest hourly measurement varies a lot based on when Anna took the baseline measurement and when she set the particle counter into hourly mode. Therefore, it’s difficult to compare how fast the particulates went down.

If you want to try and compare the speed of the drop in particulates in the first few hours, you’ll have to note the time that the filter was turned on (in the far right column). However, for speed comparisons, I think our controlled tests are much more useful (here’s an example). I’ll post more of those in the future.

The original data: The raw data for the original DIY and the cannon are in the original posts (Cannon, Original DIY PM .5, Original DIY PM 2.5). Here is the raw data for the Blue Air:






Note that the outdoor air during these 11 tests was variable; more variable than would be ideal. Ideally, the outdoor air would remain relatively stable. To analyze whether outside fluctuations affected the results, Thomas re-calculated effectiveness by looking only at the 5 days where the outside concentration did not change by more than 50 micrograms from baseline. However, that gave nearly identical numbers for average effectiveness: 91% of PM .5 and 96% of PM 2.5 (versus 90% and 96% over all 11 tests). Therefore, we're confident that outdoor fluctuations did not significantly influence the estimation of effectiveness.

Here's the data for the Philips:






There was one outlier in the Philips data: the percent reduction was much lower on 11/30 (68% and 83%). This may be because the outside concentration went from about 25 to 125 on that day; a fivefold increase. Thus, Thomas removed this datapoint from his final calculation of effectiveness. However, you can see the calculation with that datapoint included above.

Please contact us if you have questions about our methodology.
We may not be air quality experts but we strive for total honesty in the way we report data.

Are you experts in air pollution?

No. Thomas, our data guru, is a PhD student in psychology at the University of Virginia. But we're firm believers in honest presentation of empirical data. Our philosophy is that no one should believe us just because we say so. Instead, we openly publish our data and methods so you can see how we reach our conclusions and judge for yourself. And we own a particle counter.

Are you saying your DIY air purifiers work better than the expensive brands?

In our tests, our Cannon DIY outperformed a BlueAir and a Philips, so in a sense, yes! However, it's important to remember that these results are based on overnight particulate reductions in a 15 m2 bedroom, and don't take into account other room sizes or gas pollution (for example, carbon monoxide). But if particulate pollution is your primary concern (it's our main concern!) and your bedroom is 15 m2 or smaller (most are), then the DIY filters we sell perform about the same as (or in the Cannon's case, better than) the expensive brands.

Why can't I just order the filters and fans myself?

You can! We have links on our Particle Counting blog. We're more committed to spreading the knowledge that HEPA filters are a cheap way to effectively combat air pollution than we are to making money, so we'd never discourage anyone from buying the same parts elsewhere.

We just try to make the parts easier to get for people who don't want to scour Taobao for the cheapest filters. People have also emailed us saying that some stores stop carrying fans in the winter and that some HEPA manufacturers don’t sell in small orders. We buy in bulk so we can offer a low, flat rate (200RMB) that includes shipping anywhere in Mainland China. By buying with us, you also know that you’re getting HEPAs that we tested personally for effectiveness.

Where do you ship?

We ship for free within Mainland China. We can ship to Hong Kong for people who are willing to pay the extra shipping. We do not currently ship to other countries because the shipping fees would probably about double the cost!

Are you making money off this?

Not tons. So far we're making enough to pay modest salaries to the people on the team, although Thomas is still working full-time for free. Any leftover cash goes to buying testing equipment and to development of our soon-to-be commercially produced affordable air purifier.

I don't feel much air flowing out the front. Is that normal?

Yes. Our tests show conclusively that the DIY purifier still cleans the room air.

How often should I change the filter?

Short answer: If you're using our filters in China, you should change them once every 3 months with 8 hours of use a day, based on our test data. Long answer: One of our HEPAs lasted 90 days without any drop in effectiveness, then effectiveness dropped by 4% between days 100-130. It's up to you to decide whether that 4% is enough to warrant changing your filter after 3 months of nightly use. This longevity test is still running, so stay tuned to Particle Counting for updated results.

Keep in mind that this recommendation is for the Original, and not necessarily applicable the Cannon. If you'd like to see the raw data, you can download it here.

Don't see your question answered? Get in touch and we'll get back to you as soon as we can.

Smart Air is a small social enterprise that promotes DIY air filters as a low-cost solution to indoor particulate air pollution in China.

In January 2013, PhD student Thomas Talhelm wondered why air purifiers cost so much. He bought a HEPA filter on Taobao, strapped it to a simple fan, bought a particle counter, ran some tests, and published the results on a blog he called Particle Counting.

A few magazines wrote about Thomas's "re­discovery," and then the Beijing Energy Network suggested he lead DIY workshops to help other concerned Beijingers build their own.

When people said they had trouble finding the right type of fan and a trustworthy HEPA, Thomas and his friends Gus and Anna decided to launch Smart Air in September 2013 to ship fans and the best HEPAs they could find to people all over China.

Smart Air believes that if more people saw our open­ source data and testing, more people would know that clean air doesn't have to cost thousands of RMB.

The Smart Air Team

Thomas Talhelm

Thomas is the original Particle Counter and a PhD student in cultural psychology at the University of Virginia. When he's not leading the Smart Air team, Thomas studies cultural differences between northern and southern China.


Anna Guo

Anna helped Thomas assemble his first DIY air filter in 2013 and has been tolerating his incessant particle counting ever since. Now she runs tests, orders materials, and manages team projects for Smart Air. In her spare time, Anna enjoys photography, yoga, tea, and French film.


Gus Tate

After finishing a master's degree in applied linguistics at Beijing Normal University, Gus started running DIY filter workshops and managing the Smart Air website. Besides helping people breathe easy, he also enjoys juggling and doing stand up.


Ted Patterson

Ted studied music and business in the good ol' state of Tennessee. When he's not hard at work on the creative side of Smart Air, Ted plays in a band around Beijing.


Henry Zhao

Henry handles Smart Air emails and Paypal orders. A cool cat soul encased in an inconspicuous human shell, he enjoys drinking milk tea, taking Polaroid pictures, and pondering his place in the universe.


Matt Schrader

A longtime Beijing resident with experience in banking and PR, Matt joined Smart Air to help with all the boring corporate stuff. (He loves that stuff.) In his spare time Matt enjoys playing the guitar and being just a little taller than is strictly necessary.


Mag Song

Upon finishing university in Shanghai, Mag joined Smart Air for the summer before setting out for Toronto to study sustainability. Now she does business development for Shanghai and runs DIY air filter workshops for in Shanghai. She is a Beijinger and would love to see her beloved home greener. In spare time, she enjoys reading, yoga, and food hunting in the city.