kengr

As Dean himself pointed out years later, these days, if you are preparing ahead, you can do even better. HEPA air filters are common, and with them you can make a better air pump. More efficienct and easy to change the filters.

Standard fittings for furnace filters will work fine. I'd have the air entry chimney have a long vertical shaft with the air intake above the bottom and a trap to let you shovel out accumulated dust from the bottom (said trap to be *outside* the inner shelter, thank you very much).