Tuesday, August 16, 2022

8/16/2022 Make your own filter fan

One easy and affordable way to make your own air cleaner at home is with a box fan and a furnace filter. These “filter fans” can filter out the small particles that are common in wildfire or wood smoke. Particle pollution can lead to a number of immediate and long-term health impacts such as trouble breathing, asthma attacks, and lung and heart disease. Particle pollution is especially dangerous for children, the elderly, and people with sensitive immune systems.

The Puget Sound Clean Air Agency measured air pollution levels in four homes using filter fans. In smaller rooms, with the windows and doors closed, we found up to a 90% reduction in air pollution (1). Other studies have found a similar reduction in air pollution during wildfire smoke events (2).

Photo credit: Adam Petrusky, PSCAA

Supplies and Assembly

  • Box fan
    • Note: Look for a model with the controls/cords on the top or bottom of the fan. Having controls or cords in the center of the fan makes it hard to put on the filter.
  • 20x20x1 inch MERV-13 filter
    • Note: FPR 10 and MPR 1900 rated filters are equivalent to MERV-13.
  • Assembly: Tape the filter onto the back of the fan.

Important Tips While Using a Filter Fan

Testing by UL found no safety concerns with filter fans. Even so, it is important to follow these instructions:
  • Follow the box fan manufacturer’s instructions, which can include: Don't leave children unattended when the fan is in use, don't use an extension cord, don’t use near water, and don't use a damaged or malfunctioning fan.
  • If you are using your own fan, make sure it is 2012 or newer. Older models pose a fire risk and should not be used.
  • Use the filter fan in the room you spend the most time in.
  • Position the filter fan toward the middle of the room, away from walls, drapes, and dusty spaces.
  • Close all windows and doors while filter fan is in use. The filter fan won’t be as effective if pollution from outside is coming into the room. However, if it is too hot inside, you can open a window.
  • Running the filter fan in a window will result in reduced filtration and make the filter get dirty faster.
  • It takes at least 10-15 minutes to clean a small room (15’x15’).
  • The filter fan cannot clean an entire large room. If you are in a large room, place the filter fan near you so that it keeps the air around you clean.
  • Replace filters after 3 months of use or when they look dirty.



  1. Here's an even better filter and fan combo, the Corsi Rosenthal box!

  2. Arranging the filters in a cube does a great job at improving the air flow (lowering the pressure drop by increasing surface area).

    It can be a great option. Or, for the same price, you could build two filter fans that each have one filter, which could work better in a larger space. It is also the cost of a small HEPA air cleaner, which may be less noisy. All good options, depending on the circumstances.


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