Tip for 20”x20” filters on a 20” box fan: Put the filter BEHIND the fan. The suction will secure the filter to the fan, and you’ll also keep dirt off the fan m

Tip for 20”x20” filters on a 20” box fan: Put the filter BEHIND the fan. The suction will secure the filter to the fan, and you’ll also keep dirt off the fan motor and blades.