Box fan with a 20x20x1 filter makes the fan work much harder. 20x20x2 or 20x20x4 filters have much larger surface area, which is better. Creating a cube with

Box fan with a 20x20x1 filter makes the fan work much harder. 20x20x2 or 20x20x4 filters have much larger surface area, which is better. Creating a cube with four 20x20x2 is the best in terms of energy use and air output. And then you add a fan shroud for even more efficiency. 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-...