- 20x20x4 MERV12 filter. The 4-inch pleating is key here, to reduce the air resistance on the box fan.
- 1 inch dust pre-filter. This is course, low air resistance, and is for increasing the life of the more expensive MERV12/HEPA filter (so it doesn't get clogged with easy to filter dust).
- Both filters are on the intake side of the box fan. This means you don't need a bungee cord because the intake has negative pressure, the filters just "stick". It also means you keep your box fan flowing with only cleaned air.
- 20 inch box fan
- 20x20x4 MERV12 filter. The 4-inch pleating is key here, to reduce the air resistance on the box fan.
- 1 inch dust pre-filter. This is course, low air resistance, and is for increasing the life of the more expensive MERV12/HEPA filter (so it doesn't get clogged with easy to filter dust).
- Both filters are on the intake side of the box fan. This means you don't need a bungee cord because the intake has negative pressure, the filters just "stick". It also means you keep your box fan flowing with only cleaned air.
Heres a pic of my setup: https://imgur.com/a/O4I6Udx
And here's a graph this morning from my air quality sensor, after turning on the fan/filter: https://imgur.com/a/c5GMNcC
The peak at ~30ug/m^3 PM2.5 is approximately 100 AQI. The fan was on the other side of my 900 sqft house from the sensor.