Wife wants to put together an air purifier or three and she was looking at some box fan contraption idea online that uses furnace size hepa filters. Evidently she is not the only one as the filters appear to be sold out everywhere locally. We are headed out now to see what we can find that is HEPA rated. Please post any ideas you have for making something at home, hopefully on the cheap. We have some Kirby hepa vaccum bags we are thinking about sacrificing to rig up on a portable AC.