

Cost: $18–$22 per fan, $20+ per MERV 13+ filter
An easy way to add some air filtration to your space is to attach minimum-efficiency reporting value, or MERV 13+, air filters to a box fan. It is a relatively inexpensive way to boost air filtration if an air purifier is out of your budget or unavailable.
Click on this link from Colville Reservation Air Quality Program for step-by-step, illustrated instructions for making your own air purifier using two MERV 13+ filters and a box fan.
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A few things to keep in mind about this hack:
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MERV 13 filters are in short supply in some places. If you can’t find a MERV 13 filter, then it’s okay to use whatever one is available to you (eg, a MERV 11 or a MERV 9 filter)
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It does increase the noise level in the room, so if you need to shut it off to hear, that’s okay. Run it whenever you can or lower the fan setting to reduce the noise
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We suggest putting the filters on the side where air is being sucked in
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However, Pirie Associates cautions that the dirty side of the filter will be exposed and any touching of it could resuspend any trapped virus particles
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Read another set of step-by-step instructions from Tom Builds Stuff.
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Read more about the effectiveness of a box-fan air purifier from TexAir Filters, click on this link
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For variations that use only one filter go to Pirie Associates
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The one-filter version requires more frequent filter replacement and will use more energy. However, if only one filter is available, then it’s still possible to make an effective purifier with just one
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