“If you’re in a hurry, this post says that if you strap two HEPA filters to a box fan, it will clear the air of basically all the particles we can measure, and it will do it faster than a commercial filter that costs twice as much.”
Two HEPA filters and a bungee cord on a box fan beat a $100 branded purifier. The branded unit uses one small proprietary filter that costs $25 to replace. That is the business model. The fan is not the product. The filter subscription is.