Even cheaper is the DIY Corsi-Rosenthal box. We make a couple every few months and it does make a huge difference! Worked wonders during the wildfires a couple

Even cheaper is the DIY Corsi-Rosenthal box. We make a couple every few months and it does make a huge difference! Worked wonders during the wildfires a couple of years ago https://cleanaircrew.org/box-fan-filters/ https://cleanaircrew.org/box-fan-filters/