Strategies to Reduce Exposure to Wildfire Smoke during the COVID-19 Pandemic | CDC

The west coast is currently experiencing some of the worst air quality in the world. Steps must be taken to reduce exposure to smoke and fine particles.

I've mentioned the DIY box fan air cleaner before and I still recommend it. especially since commercial HEPA filters and air cleaners are sold out at present. The triangle configuration shown is Important in reducing air resistance, box fans aren't meant to run with a filter. If you just tape a filter flat to the fan you'll burn it out quicker and it might not move enough air to improve indoor air quality.

Speaking of furnace filters, MERV 13 is the minimum rating needed to filter smoke. A lesser filter isn't worthless however. Larger soot particles will still be removed by lower rated filters.

Upgrading your furnace filter can help improve indoor air quality. However if your furnace is fitted with a 1" thick filter you should not exceed a MERV 8 rated filter. With too much restriction you run the risk of damaging your equipment. Some air handlers can be easily modified to accept a thicker filter. A thicker filter has less air restriction because it has larger pleats and more surface area. This would allow you to use a higher MERV filter without risk.