How to Make a DIY Air Purifier

How can we make a homemade DIY air purifier? Air purifiers can be extremely expensive, but they don’t need to be. After researching how different air filters work, I concluded that a HEPA filter is all that’s needed to make an effective air purifier that can capture viruses, wildfire smoke, dust, pollen and more.

Given that most air purifiers sell for thousands of dollars, I thought I’d try making my own homemade DIY air purifier.

WATCH: How to Make Your Own Homemade Air Purifier

3 Steps to Build Your Own Air Purifier

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Hold Up: Do DIY Air Purifiers Actually Work?

I’ve tested this DIY air purifier for over 1000 hours! The data shows they work! They are effective for the dangerous tiny PM2.5 particles including what you find in wildfire smoke and even tiny viruses! What’s more, they even outperform many of the big brands. With that out of the way, in this post, I’ll explain exactly how to make your own homemade DIY air purifier.

DIY Purifier Test AQI PM2.5

How to Make a DIY Purifier

#1 Buy a fan

It’s important to buy a fan with a flat front or back so that the HEPA filter you buy fits flush.

Fans with flat fronts usually have a recessed motor unit, so look for that. Here’s the one I bought below. Box fans also work great.

diy air purifier fan

#2 Buy a HEPA filter

For my very first homemade air filter, I first bought this one for ~US$16:

HEPA filter for homemade DIY air purifier

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 airflow. Because I buy it in bulk and ship it through the shop for my social enterprise, it costs less than the first HEPA I bought. I’ve tested this HEPA filter with my particle counter, so I know it works (watch the live DIY filter test here).

#3 Prepare your fan for the HEPA filter

If your fan isn’t 100% flat – this is where the DIY filter fun starts! The fan I used wasn’t entirely flat, but by removing the front grill using a set of pliers, I was able to create a flat surface.

Step 3 in making a DIY air purifier

#4 Strap on the HEPA filter

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

If you have a metal bar in the middle sticking through the filter, don’t worry! 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.

Rear view of DIY fan air purifier
front view of HEPA attached to make DIY air purifier

To really improve your homemade fan’s performance, you could try taping your HEPA filter to the fan to avoid any leaks around the edges. Here’s a Corsi Rosenthal Box Fan where the fan is taped to the filters (multiple ones!) using masking tape.

#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. 

DIY 1.1 Air Purifier Filter HEPA

Want to Make a Strong DIY Air Purifier?

Since we shared this cost-effective DIY air purifier with the world, the Corsi-Rosenthal DIY air purifier has also appeared. This DIY air purifier uses multiple furnace filters (MERV 13 and above) with a large box fan. This type of design has a more powerful CADR, can be assembled in just 15 minutes, and costs around 100 USD.

Learn more: 4 things to know about the Corsi-Rosenthal (CR-Box) Fan »

Bottom Line: How to Make a DIY Air Purifier

#1 Buy a fan

#2 Buy a HEPA filter

#3 Pull the grating off the front of the fan

#4 Strap on the HEPA

#5 Admire your new DIY air purifier

Smart Air

Your next question is probably, does this DIY air filter work? See a live test here. Here are a few other important questions:

  1. Filters: What combination of filters do I need to protect against everything?
  2. Stronger fan: Tests with the DIY Cannon
  3. 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.

A Simpler Way to Breathe Clean Air 

Smart Air’s founder and University of Chicago professor, Thomas Talhelm, created the first DIY air purifier 10 years ago that shook up the air purifier industry. Thomas then created Smart Air, a certified B Corp committed to combating the myths big companies use to artificially inflate the price of clean air.

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We at Smart Air not only educate but also design and manufacture empirically backed, no-nonsense purifiers for homes and businesses, that use the same HEPA filters for a fraction of the cost of big companies.

Shop Smart Air’s Lineup of Cost-effective, Data-backed Air Purifiers

Smart Air’s award-winning Sqair bedroom air purifier

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

48 thoughts on “How to Make a DIY Air Purifier”

  1. Thanks for sharing. Does this work for filtering out the Covid-19 virus particles in air aerosols? If I use such a purifier while I stay in a hotel room where the windows cannot be opened, is it going to be effective?

  2. A humidifier’s main purpose is to restore moisture to the air in your house. It achieves this by injecting water vapour into a room, which can be visible or not. Continue to fill a reservoir with water to keep the humidifier operating. The mechanism converts the water into a fine mist and expels it into the surrounding air. v Humidifiers are most effective in dry environments because they replace moisture in the air. The Most Effective Air Purifier Living in an arid area can cause dry skin, throat irritation, sinus problems, nosebleeds, and breathing difficulty. A humidifier can assist.

  3. Is there any reason why your filters are relatively very thick compared to other air purifiers? I definitely like that your filters are thick – it feels robust. But I noticed that other HEPA filters are usually thin and made of less paper. Does it mean that your filters are much more robust & has better longevity or is it a simple trade off in cost-effectiveness (i.e. cheaper material but equal effectiveness)?

    • Great question Ken. Thicker filters mean deeper pleats (folds) in the HEPA filter. Overall, this means more HEPA filter material can be packed into the HEPA filter, allowing for a higher airflow and longer lifespan of the filter.

      The reason Smart Air’s filters may appear thicker is because we design all filters to have maximum airflow – thicker means higher airflow.

  4. Seeing as we can’t search through comments, I apologize if this has been asked:

    How much difference does it make if we don’t pull the grating and knobs off, or if the filter is not the same size or cannot be fastened flush with the fan?

    It seems odd to me that filters will be the same dimensions as fans as they come in all different shapes and sizes!

    • If you look at the photo you can see that all that matters is that the filter is as big as the whole area that air comes out of. So that circular indented area where the fan blades are, your filter just needs to be at least as big as that. It won’t matter that the filter is bigger.

  5. If I use a hepa filter for my furnace, and have the furnace fan on all the time, is this an effective air purifier?

    • Hi Shea, the only issue is that in order to push enough air through the filter, you need a fan powerful enough. For sure if you use a HEPA filter there, it will help to clean air going through, but is the amount enough to clean up the whole room, that depends on how strong your fan is and how large your apartment is.

  6. Thank you so very much Thomas because you have saved me some financial hardship trying to come up with the money for a purifier. Temporarily out of work and the thought of needing at least 3 devices for my home then the cost of filters. Oh gosh! Your DIY air purifier came at the right time for me. May God so richly bless you…

    • Hi Mira, the plug on our DIY fan is not the same as Australia’s plug type, but with a simple adapter (similar to a travel adapter) you will be able to use the fan in Australia!

  7. hello, I have purchased a diy1.1 air purifier. Which side of the hepa filter should face the fan?

  8. Hi! I’m in ACT Australia and currently due to extreme conditions, hundreds of fires are burning 1-3 hrs away. This is blanketing our city for weeks.
    Needing to attempt to make this amazing alternative as I cannot breath easy in my smokey apartment with my children.
    My question is, after I purchase my fan and hepa-filter, can I also attatach a carbon filter as well as 2x general filters to the one machine? I would be very grateful to know exactly the right combination and order (if there is one) please…so that all the ‘bad’ is captured effectively.
    Thank you so much!

    • Hey Britt, can’t imagine what you and your family are going through in Australia because of the fires!
      To answer your question, there can only be 1 filter attached to the fan at each time — either a HEPA or a carbon filter. If you attach more than 1 filter, it will not be effective because a fan’s strength isn’t enough to support both.

  9. Thanks for this! I was inspired to build my own. Q: do you recommend combining HEPA and activated carbon filters with a regular box fan, or would that put too much strain on the motor?

    I’m running it with both at the moment, but I don’t even know if it’s pulling the air through at sufficient volume to be effective, since I can’t feel the air flow pushing out the front.


    • Hey Rory, you can combine a HEPA and carbon filter on a box fan but the best way to make sure it is effective is to get an air quality monitor!

  10. Hi, this maybe a silly question. I just made a DIY air purifier similar to instructions here. How much of air flow should we be able to feel at the front of the HEPA filter ? Little or none at all as I am getting almost none.

    • Hey Muhammad! This is a very common question for DIY air purifiers. Even if you can’t feel a lot of air coming out of your DIY, it doesn’t mean it’s not working. With the original DIY that Tom made, it also felt like very little air was coming out, however tests proved it to be effective. Check out this video of Tom showing this:

      To ensure you’re getting the maximum air possible out of the purifier, make sure there’s a good seal between the fan and the filter, and that no air is leaking out of the back of the fan.

      Breathe safe!

      • Hello! I had a similar problem to Muhammad’s – little to no air flow out of the front of the filter and significant flow out of the back of the fan (even after taping up all of the side vents in this particular desk fan.

        What do you recommend to correct for this? I’m in the USA, so I don’t believe I have affordable access to the same fan listed in the instructions in this blog post.

        • If you’re in the USA, then you’re in luck! I suggest you get yourself a box fan and a large furnace filter. These fans are extremely powerful and very affordable in the US. They should be a great option for you!

  11. Hi Thomas,I want to buy your HEPA Filter through Taobao website. However i have a big question : the last product is an air purifier machine or a fan having air purifier function. Is this product still a fan? Does it make cool anymore?

    • Hey Vivi, Tom’s out doing nerdy stuff so I’ll reply on his behalf! With the HEPA filter attached, the airflow is much less than a regular fan, so these DIY purifiers don’t have a strong cooling effect. However since the HEPA filter is detachable from your fan, you should be able to remove the HEPA filter at any time to turn the DIY air purifier back into a fan.

  12. Hi, I wanted to back/order the Squair on Kickstarter but am I one day too late? The photo says it ends on July 5th, which is today, but I can’t seem to find a link to order… thanks!

  13. Finally the fan+filter is to be fitted as a fan (pumping air towards you) or as an exhaust fan (pumping air outside) ?

      • thanks a lot, I will do it. we are also interested in becoming a tester and create data for México and all LatAm countries. we are an IOT network that wants to help solving air quality problems in our regions. this is our website , let us know how we can collaborate.

  14. Hi. Where’s the best location to place the diy air purifier? I’m not sure if it needs a different air path vs the regular purifiers. Thanks. Janet

  15. Hi there. I have done a similar thing ihere in Chaing Mai but instead of using a Hepa filter I used Filtrete air con paper made by the company 3m. Do you think this would also be an effective way of cleaning the air?

    • Yes, you can use the 3M AC filters for your air conditioning! We have actually tested this, but are yet to write up a report on it. What we found was that using the paper on air conditioners was effective at removing around 80% of PM2.5 in a small 10sqm room. However the effectiveness will depend greatly on how powerful your AC is and how often you change the filter paper.

    • where in chiang mai did you get the filter paper? Everyone of my mates leaves this time of year because of the smog. I will be returning later in the year but i want to prepare for next year

  16. I really enjoy that you are sharing technical proof in the article. I do a lot of drywall (gypsum) wall work and have been doing this same thing for almost 20 years. I use the 20in box fans that are sold everywhere (in America) for $25 or less and furnace air filters $7-20 depending on quality and vendor. This allows work to be done in single rooms with the doors closed keeping the dust from invading the rest of the home. For $30-40 (US) I have great air cleaning comparable to commercial units costing $130-400. I also get very affordable filters

  17. I am from Malaysia.
    In the consideration of expensive international shipping cost for a cannon fan, I would prefer to purchase the fan locally. Please advise me if I could use an
    exhaust fan with the air flow rate at 830m3/hour, using both HEPA filter and activated carbon filter for purifying my newly renovated house?

  18. Do you have your filters and such available for purchase in North America? I’ve enjoyed navigating around your website! Thank you for all the work and publishing the information.


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