Abstract: Airhouses for supplying conditioned air in controlled amounts to the interior of large enclosed buildings. An improved air inlet, burner and damper construction adapted for utilization with both newly constructed and existing airhouses is provided. A burner assembly and an outside air inlet are incorporated in a unit adapted to be affixed to the airhouse. A building return air inlet provides communication between the airhouse and the interior of the building. Shear dampers or valves of equal flow capacity varying linearly between open and closed positions are provided in the outside and building return air inlets. The dampers are controllably interconnected to operate in opposition so as to admit a uniform combined volume of outside air and building return air to the airhouse. The burner assembly and outside air and building return air inlets are sized so that air entering the airhouse through the burner unit and the outside and return air inlets are at substantially equal velocities.