If you go the old school "filter taped to box fan" route, be sure to add a shroud for the corners, as blade tip turbulence there actually causes reverse air flo

If you go the old school "filter taped to box fan" route, be sure to add a shroud for the corners, as blade tip turbulence there actually causes reverse air flow. See the article by the 'R' of Corsi-Rosenthal. https://www.texairfilters.com/how-to-improve-the-efficiency-of-the-box-fan-and-merv-13-filter-air-cleaner/ https://www.texairfilters.com/how-to-improve-the-efficiency-...