How to build a DIY air filter with a box fan, tape, and MERV13 filters – CorsiRosenthal Box
QuickStart Diagram – How to build a DIY air purifier
20x20x1 or 20x20x2 MERV 13 furnace filters (1, 2, 4 or 5 filter designs available)
This Old House assembles a 4 filter air cleaner, using 20x20x2 MERV13 filters and a box fan. This video is cued up to start as they build, but start at the beginning for a very informative discussion of how the system works.