An air return bulkhead comprising a base; a return air duct extending outward from the base, the base and air duct defining a bulkhead return air chamber, the duct comprising a first wall, a second wall, a third wall, a fourth wall, and a fifth wall joining the other walls; at least one return air inlet notch formed in the air duct fourth and fifth walls; and means for producing turbulent return air flow through the return air chamber, said means located downstream from the at least one inlet notch. The bulkhead further includes air dam positioning means on the first and second walls. Individual air dam members are slid in the positioning means to be removably mounted along the bulkhead.