an impingement device for preparing food product comprises an enclosure having a conveyor received therethrough for conveying food product through the enclosure . positioned within the enclosure and about the conveyor portion therein are ducts for impinging gas against the food product , a plenum connected to the ducts for supplying gas to the ducts , and an impeller assembly for recirculating the gas within the enclosure . a heating source or cooling source is provided within a chamber on the opposite side of the plenum from the ducts and controls are provided for regulating the temperature of the heat or cooling source . the plenum is spaced inwardly from the walls of the enclosure to provide return flow around the plenum .