Exactly what I do, but with a 5", 20x25" MERV 16 filter. I run two of these on box fans when it's smokey in the summer, and it works very well. Box fans do get

Exactly what I do, but with a 5", 20x25" MERV 16 filter. I run two of these on box fans when it's smokey in the summer, and it works very well. Box fans do get loud though.