Make Your Own Box Fan Air Filter

Bronze Tip Medal for All Time! 75 Tips
September 13, 2020

Make Your Own Box Fan Air FilterWith all the wildfires right now air quality has gone down throughout the west coast. Here's an easy way to make a room air filter out of a box fan and a furnace filter.


For best results use a HEPA filter with a MERV-rating of 13, an FPR-rating of 10, or a Filtrete MPR rating of 1000 or better. These are often advertised as "allergy" or "health" filters.

Total Time: 5 Minutes


  • 1 20x20 box fan
  • 1 20x20 allergen rated furnace filter
  • tape
Make Your Own Box Fan Air Filter
Make Your Own Box Fan Air Filter - box fan


  1. The idea is to mount the filter on the box fan so that it is on the air intake side of the fan. The motion of the air will pull the filter up against the fan.
  2. Make sure that the air is flowing through the filter in the proper direction. You want the arrow on the filter to match the air flow through the filter.
  3. You can use tape to secure the filter to the fan if you want. Or simply position it when you turn on the fan.
  4. If you use your filter for an extended time be sure to replace it regularly. Most furnace filters should be okay for about 3 months of use.
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  6. These kind of filters work best within a single room of your house with the doors and window closed. The air should recirculate in the room through the fan getting cleaner on each pass.

Note: Do not use this type of filter in an open window. It won't be able to filter enough smoke out of the air to make it worthwhile. Don't use the fan for an extended period. Check to make sure it isn't overheating. Don't leave the fan unattended. Turn it off before you go to sleep or leave the room. Don't use it in a bathroom or kitchen where it might get wet.

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Gold Post Medal for All Time! 519 Posts
September 7, 2006

Just picked up some clever filters for my box fans from the thrift shop - They are shaped like large shower caps and made out of a "pellon" material. . .

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