The problem of air intake contamination from nearby exhaust vents has developed increasing importance in recent years in light of the emphasis now placed on environmental protection and industrial safety. Also, energy recovery from exhaust air by regenerative heat exchangers is presently a common practice for medical facilities, and as fuel costs continue to rise it is probable that this form of energy recovery will become economically justifiable in other situations as well. The need for passing both inlet and exhaust air through a single heat exchanger can dictate a shorter separation between inlet and exhaust vent locations, and this in turn can only serve to aggravate inlet air contamination problems.