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Comment by breput

3 years ago

Big Clive made a video and wrote an OpenSCAD script[0] which allows you to 3D print a base and adapter to convert a regular 120mm computer fan into a "true" HEPA air purifier.

You might already have a spare 120mm fan laying around - I am using a $8 ARCTIC P12 fan[1] which is very quiet and is designed to work with high static pressure. The generic filters[2] are two for $17, (supposedly) H13 grade, available from a number of suppliers, and last a very long time. You could use them one at a time but I stack the two filters on top of each other and seal them with electrical tape for more surface area.

The fan isn't super powerful (56 CFM) and the appearance is not as polished as commercial models, but it does have a certain aesthetic to it. The area where I live rarely has any air quality issues but I have noticed it really cuts down on dust.

[0] https://www.youtube.com/watch?v=6Vmh2Ip2Vxg (script in the Description)

[1] https://smile.amazon.com/gp/product/B07GB16RK7

[2] https://smile.amazon.com/dp/B08N1FP2WT

8 comments

breput

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steamer25  3 years ago

Matthias Wandel recently did some experiments over several options. A decent furnace filter, when duct-taped to a box-fan, did surprisingly well:

https://www.youtube.com/watch?v=rDZ9yUdM2wA

It turned out that my local hardware store had a similar pre-manufactured offering with a slightly less Jerry-rigged aesthetic. We bought one for my son's allergies but I also noticed an improvement on the whole upper floor of our house. Box fans can move a lot of air. Furnace filters are cheap commodities with a large cross-sectional area that also allow a fair amount of flow.

  • breput  3 years ago

    There seems to be two main use cases for a room-sized air purifier:

    If you live in a polluted city or are affected by wildfires, having a box fan-sized model is almost a necessity. It is going to be noisy and unsightly but undeniably more effective. Having a few furnace filters laying around for air quality emergencies is probably not a bad idea.

    For day to day use in a low pollution area, where dust or pollen is the major concern, I really like the little 120mm fan purifier. It runs 24/7, unobtrusively, and is really effective for what it does.

    • vl  3 years ago

      Surprisingly, there are ultra-quite full-size fans as well. I bough Vornado fan from Amazon, and this is one of the best devices I ever had. On first two speeds it’s basically silent, I use it 24/7 to ventilate room with bad air flow in my house. It’s also Alexa integrated, but I never can remember the commands.

aftbit  3 years ago

Thanks for sharing this! Can you provide the values of the variables for that exact linked filter and fan? I'd like to print this while I wait for Amazon shipping. I bought ASIN B07GJG285F instead - same fan, but faster shipping for me.

  screwhole=5;     //fan screw hole diameter (5)  
  filterhole=92;     //HEPA filter hole diameter  
  thickness=1.5;  //Thickness of plastic layer (1.5)  
  insert=10;          //Length of insert into filter (10)

  • breput  3 years ago

    You'll definitely want to bump thickness up to 2.0 mm for more rigidity. Otherwise just measure the diameter of your filter and maybe round up slightly.

    I put a layer of electric tape around the flange where the filter adapter inserts into the filter and it makes a very nice airtight fit. Finally, just print it with the big end facing down and you shouldn't need any supports.

    screwhole=5; // fan screw hole diameter (5)

    filterhole=59; // HEPA filter hole diameter

    thickness=2; // Thickness of plastic layer (1.5)

    insert=10; // Length of insert into filter (10)

KennyBlanken  3 years ago

That air filter will move such a small volume of air, it's basically useless unless you're in a small closet.

  • breput  3 years ago

    Well, my experience refutes that opinion, but yes, it sized for a smaller room or less polluted larger areas.

    My office is approximately 12' x 12' x 8' or 1,152 ft³. That means the room's air would (theoretically) completely pass through the filter every 20 1/2 minutes. As the article explains, even the lower quality filter in the Ikea air purifier is so close to 100% efficient that it isn't worth worrying about, so completely filtering the air three times per hour is nothing to sneeze at...

    And the cost is negligible - the fan might cost $0 to $10, filters are $20/year, and electricity usage is around 2 watts or probably under $2/year.