DIY air filter for fire season
Record fire conditions in California, Oregon, and Washington in Sep 2020 plunged all of the Northwest in choking, hazardous levels of smokey haze. For air quality details see AirNow and the Fire and Smoke Map. There isn’t much you can do to escape. Official advice is basically just stay inside, turn your air conditioner on recirculate, and run your air purifier full time.
What if you don’t have a HVAC system, recirculate option, or air purifier?
Basically its miserable… but here is a viable DIY option to clean your indoor air made with a box fan, furnace filter, and duct tape.
p.s. more recently it has been discovered that running this type of filtration also helps protect from Covid in enclosed spaces! If you have four air filters available, build a more advanced Corsi-Rosenthal box (or collection of DIY resources from Clean Air Crew). UC Davis has published some research confirming the effectiveness of these DIY filters.
Step 1: Get Fan
Do you have a box fan? Great. Measure it, usually they are about 20” x 20” square.
Step 2: Get Filter
Wild fire smoke produces fine particle pollution (2.5 micrometers and smaller), so you need a high quality furnace filter, something like Filtrete Healthy Living that uses electrostatic charge to capture particles. Look for a MERV rating of at least 11, MERV 12 or higher is better.
If you are in a pinch and not using your furnace, you can just grab it out of your system.
If you go to the store, look for a size that will cover your box fan. Ideally, it would be 20”x20”x4” size fitting perfectly over your fan. Deeper filters provide better flow and last longer, but the standard 1” will be fine too.
However, that ideal size is rare and if you are in a smokey area filters sell out fast–so just find anything that covers the fan with the highest MERV rating. I find that odd sizes are usually cheaper than common ones, so I used 20x30x1 because it was $5 cheaper than 20x20 for the same quality!
Step 3: Duck Tape!
The filter will have an arrow showing which way the air should flow through. Lay the filter onto the back of your box fan with the arrow pointing into the fan. Use a few pieces of duct tape to secure it directly to the fan.
Step 4: Use It
Obviously. The picture below shows a fresh filter next to one used for 24hr during horrible smokey conditions.
Another tip: get a spray bottle with clean water and spritz the air around your house every so often. Moisture particles help pull smoke pollution out of the air.
