On: Reverse engineering my Coway air purifier to ditch the cloud

a box fan and a furnace filter.

It works really well and even more - it works better than any purifier even if you just duct-tape the filter you have to a box fan.

To people who think this is a joke, it isn't: https://en.wikipedia.org/wiki/Corsi%E2%80%93Rosenthal_Box