How to make a DIY air filter with a box fan
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If you’re in an area with wildfire smoke and don’t have access to a commercial air filter, DIY air cleaners can offer you some protection if assembled correctly.
The U.S. Environmental Protection Agency has studied the use of homemade air filters and offers the following tips on how to assemble one.
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How many DIY air filters do you need?
According to the EPA, more than one air cleaner can be handy if smoke is very thick or your home is not well sealed from the outdoor environment.
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But one may be enough if you can designate one room in your home as a cleaner air room that people spend time in. You can also move the filter from room to room.
Washington Post health reporter Lena Sun shows the steps in making a do-it-yourself box fan air filter, also known as the Corsi-Rosenthal Box, on December 21, 2022 in Washington, DC. (Photo by Michael Robinson Chávez/The Washington Post via Getty Ima
What you’ll need
- 20" x 20" air filter (EPA suggests an MERV 13 rating)
- 20" x 20" box fan (Only use certified fans with UL or ETL marking, 2012 model or newer)
- Clamps, duct tape or bungee cords
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How to assemble it
- Attach the air filter to the back of the box fan using either clamps, duct tape or bungee cords.
- Check the filter for the direction of the air flow and make sure the arrow is facing the fan (it’s marked on the side of the filter)
- Replace filters when dirty: The EPA says DIY air filters are almost completely ineffective with dirty filters.
What not to do
- Don't leave children unattended when the fan is in use.
- Don't use an extension cord.
- Don't use a damaged or malfunctioning fan.