@denzie I have HEPA filters in every room on top of the MERV13 furnace filter. they make a huge difference in keeping the indoor air free of PM2.5 particles. I'm so glad you were able to use those in your home.

I learned a neat trick from a gal in Calgary for extended smoky periods. she added a carbon pre-filter to her box fan + HEPA filter. she placed it in a window, sealed around the edges and blew outdoor filtered air inside. (Because after a couple days you need oxygen in the house.) I built one and it really works!