Abstract: The present invention is a direct fired unit heater which includes a lower combustion chamber which communicates with an upper fan assembly which mixes combustion products with ambient air and discharges this laterally from the unit. The fan assembly has two cylindrical fans each with different critical speeds. One motor drives both cylindrical fans and is adjustable so that at a first higher speed it is within the operating range of both fans. At a lower operating speed, it is only within the operating range of the upper cylindrical fan. The upper cylindrical fan acts to pull in room air and discharge this. Thus, the blower operates continuously thereby destratifying the room air. When the burner operates, the motor speed is increased to act within the operating speed of the lower fan assembly. This lower fan assembly thereby pulls in the combustion products and discharges these along with the ambient air. The size of the cylindrical fans are designed to provide appropriate mixing for a direct fired unit.