Abstract: A reusable air filter assembly for use in forced air heating and cooling systems includes an inlet stage filter medium consisting of a single layer of fabric woven in an egg-crate pattern and of relatively coarse polypropylene yarn, an outlet stage filter medium consisting of two layers of fabric woven in an egg-crate pattern of relatively fine polypropylene yarn and a precipitation chamber between said inlet stage and said outlet stage defined by a corrugated aluminum wire screen, with the precipitation chamber having a thickness, in the direction of air flow through the assembly, which is at least equal to the combined thickness of the inlet stage filter medium and the outlet stage filter medium. The filter assembly is supported in a corrosion resistant frame by opposing grid covers of expanded metal having a low friction coating thereon.