DIY Cannon: Better, Faster, Stronger

Ever since I started my DIY filter 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:


DIY Purifier Fans Test


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:


DIY Purifier Cannon DIY Filter


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:


DIY Filter Cannon Air Purifier Test Smart Air


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

DIY Filter Cannon Air Purifier Test Smart Air

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.)


DIY Filter Cannon Air Purifier Effectiveness


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

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.


DIY Filter Air Purifier Effectiveness Test


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.)

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:


DIY Filter Air Purifier Speed Test


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.

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?

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.

[accordion-item title=”Cannon Original Data and Methods” state=closed]

Here is the raw data for the five Cannon room tests.

Calculation method: As always (1,2), to calculate effectiveness, I average 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 as reduction from outside because indoor air is cleaner than outdoor air.

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




In the raw data, you can see that some days the air pollution outside fluctuated a bit. The most stable day was probably 9/25. The effectiveness numbers that day are also very close to the average of the five tests.

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: My 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 my data comparing the two over 70 measurement occasions.

Interpreting the speed of the drop: Thee 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 up for hourly mode. Therefore, I caution against interpreting the exact time it takes the counts to drop too closely.

Instead, to answer the question of how quickly the counts go down, the controlled, minute-by-minute test is much more useful:

Controlled minute-by-minute test

To get the minute-by-minute tests, we performed controlled tests. First we put the DIY filter (not turned on), particle counter, and a lit stick of incense into Anna’s bathroom. She sealed off the fan on the ceiling and the door to keep the environment controlled.

Pollution source: Anna ran tests to determine the length of incense that would burn completely in 20 minutes (8.3 centimeters). On average, burning the incense raises the 0.5 micron counts by 40,000. It raises the 2.5 micron counts by far less–by as little as 100. This demonstrates that the burning incense is releasing particles that are almost all smaller than 2.5 microns.

Turning on the filter: After 20 minutes (when the incense extinguishes), the DIY filter is turned on using an extension cord that goes under the door and outside the room. This means we do not have to open the door, which would affect the air quality and bring undesired noise into the experiment. After that, we let the DIY filter work for the remaining 40 minutes. (Unfortunately, the particle counter sometimes fails to save a few minutes of data at the beginning and end, so the data below is somewhat shorter than 60 minutes.)

Machines: The Original DIY is the same kit we are shipping from Smart Air. The Cannon is also shipped from Smart Air.



Control condition: We also ran tests without a filter (column 1 above) to see whether the numbers drop naturally–even without a filter running. The no-filter test showed that the numbers do drop a little bit on their own (about 9%), but the numbers are quite different when a filter is turned on.



Free Guide to Breathing Safe

Want to learn more about breathing clean air? Join thousands more and stay up to date on protecting your health.

26 thoughts on “DIY Cannon: Better, Faster, Stronger”

  1. Two things I have noticed that could make a big difference.. First it appears it is not sealed which mean that ” some ” air will most likely escape around instead of going through which could alter your results. I don’t believe you ever mentioned what type of filter you are using. Size of course being an issue , ideally you should be using a Merv 13, a 4″ since the larger surface area will cause less resistance and allow for the fan to undergo less stress trying push air through it and in turn allow for a decreased reduction in air movement over a standard 1″ or 2″ of the same type. Have you considered creating a box around the fan to seal it in?

    • Hi Ryan,

      We no longer have the Cannon for sale. It’s been superseded by The Sqair. We created the Sqair as a replacement for the Cannon to be quieter, more effective, better looking and with a bigger HEPA filter. Upgrades all round!

  2. I was thinking of buying xiaomi 3h but this looks promising, but i’m only worried if this is loud? how does this DIY compare to store bought purifiers in terms of noise?

  3. Hi, live in Australia where we are unfortunately exposed to bush-fire smokes in this season.

    Is it critical for the filter to be tightly applied against the outside rim of the canon, or will a few mm gaps between the filter and the canon in some places badly compromise the performance as it leaks unfiltered airflow?
    My HEPA filter doesn’t have an outer frame and therefore flexes in places under the pressure of the fan.
    The low-tech approach would seam to suggest that we aren’t after an airtight bond between the two. Are you able to confirm?

    • Hey Steph, great to see you DIYing a solution for the Australia bushfires. A gap of a few milliliters will affect the effectiveness of the purifier quite dramatically. It will still work with the gap, but it’s effectiveness at cleaning the air will be lower that if there’s a tight fit. I suggest you deal the gap with some tape around the filter as another DIY fix!

  4. Hi,
    My city has an average PM2.5 of 40 to 50 ug/cubic metre. On top of it, there are construction activities going around my residence. So I expect PM2.5 at my house to be around 70 ug/cubic metre. Will the cannon DIY or DIY 1.1 be able to bring down the PM2.5 in my residence? with the above figures of PM2.5, how much PM2.5 can I expect if I use cannon DIY air purifier?
    Thank You

    • Hey Shriram, great question! The answer really depends on two things:
      1. How big your room is
      2. How well sealed your room is

      The DIY is good for a 15sqm room, and the Cannon (when we sold it) was good for 30sqm. We now also have the Sqair air purifier which is a replacement for the Cannon and can clean a 40sqm space when running on high. Look at the size of your room first before deciding which purifier to buy!

  5. Just out of curiosity, will the horizontal air flow of the canon and DIY have any say on the quality of output? Most air purifiers suck in air horizontally and blow it out the top. The Canon and DIY both can be made to face whosoever is sitting in the room. While they no doubt bring down ambient air pollution, will pointing them straight at the face help? The air going down the nose is what counts, after all. I am guessing doing so while sleeping might present some advantage over the regular stock?

    • I sometimes do this when I’m travelling out and about Parth! If I’m in a hotel without air purifiers, I’ll take a DIY1.1 along, and put it right on my bedside pointing at my face. You’re right that the closer the air purifier is to your face, the more clean air you’ll likely get. We’ve written about and reviewed personal air purifiers in the past, you can check out just how close you need to be to the air purifier there.

      As to why most purifiers suck in from the side and blow out the top; that’s because most purifiers use a centrifugal fan, unlike the axial fan in the DIY and Cannon. It’s a different type of fan, but does exactly the same thing: pushes dirty air through the HEPA filter, letting clean air out the other side ?

  6. Hi, I am really interested in the accessibility of homemade air purifiers to vulnerable populations. Is there any peer reviewed data supporting your findings? Thank you.

    • Great question Marissa! Our data is yet to be peer reviewed, but we’ve published it open source to allow others to analyse and scrutinise the data.

      What we do have is peer reviewed articles stating how air pollution affects the health of vulnerable populations, as well as peer reviewed articles showing air purifiers reduce particulate pollution.

  7. Would like to order HEPA and carbon filters, do you have any recommendations for comparable fans to the Cannon that could be purchased in US (Avoiding high international shipping)

    • Hey Paul, we’re working on an article to make it easier for people just like yourself to find comparable fans to the Cannon, it should be out fairly soon!

      If you’re in the US, then box fans are a very good option for a cost-effective air purifier, just make sure that the HEPA is bigger than the area of the fan. Stay tuned for that new article on DIY purifiers.

        • Thanks for following up Dennis! The article in question seems to have got lost in the weeds, and I’m not sure where it went! In short: the Cannon fan has an airflow of approximately 800-1000 cubic meters per hour (when it’s operating as a fan), so if you can find a fan with comparable numbers that should give you the same effectiveness as the Cannon.

    • Hi Pavel, we can certainly ship to Russia! The HEPAs we use are H12 HEPAs, which means they get at least 99.5% of all particles. Send us an email with what you want to get an estimate for shipping costs to Moscow.

  8. Looking forward to ordering a filter and using in Thailand. But…

    Do look you have any data on the decibel level of the two different styles of filter (original and cannon)?

    I have a big bedroom that is about 24 sqm and living room about 38 sqm

    • Hi John! That’d be awesome if this could help get you some clean air in Thailand. Noise level data is in this post:

      Bottom line there: The Cannon is about as loud as the Blue Air and Philips on high. But if it’s too loud for your tastes, the test results on low and medium still found 90% reductions in this same room, so those are good to use too.


Leave a Comment

Smart Air low cost purifiers

Smart Air is a social enterprise and certified B-Corp that offers simple, no-nonsense air purifiers and provides free education to protect people from the harms of air pollution. We are proud to be the only certified B-Corp dedicated to fighting air pollution.

Certified B-Corp air purifier company