Grumpy Old Geeks Topics Homemade air purifiers Topic Homemade air purifiers 3 mentions in 1 episode The hosts discuss attaching furnace filters to box fans to filter indoor air. Mentions 467: A Desire for Desires Aug 29, 2020 48:55 It's called Better Box Fan Air Purifier. 49:16 People are using furnace filters and slapping them onto box fans. 49:33 It's a cool little box fan air purifier.