Abstract: A heated air makeup unit comprising a heating chamber with a modulated furnace one or more non-modulated furnaces air temperature control and efficient furnace operation over a wide heating rate range. The utilization of indirect fired furnaces in the heated air makeup unit is disclosed. A control system is included to provide control of heated air temperature to within +/?1 F.° using continuous control of the heating rate of the modulated furnace and stepwise activation and de-activation of the non-modulated furnaces in response to heating demand. A programmed combustion air flow controller programmed to provide optimal airflow for any gas flow in a flow range of a modulating gas valve is provided to assure combustion efficiencies of at least 83%.

Abstract: A heated make-up air system comprising a duct structure having a direct gas fired burner mounted therein. Adjacent the burner there is provided an opening for permitting air to flow there through. Mounted adjacent the opening one or more pivotally mounted panels or profile plates. The moveable panels or profile plates are spring-biased to assume a normally closed position. However, the moveable panels are moveable from the closed position to an open position in order to control air flow through the duct structure and past the burner.

Abstract: A heated air makeup unit comprises a duct structure having a surrounding wall, a fan for moving air through the duct structure, and a gas burner mounted in the duct structure for heating air being moved past the burner. A pair of laterally spaced converging air-directing plates are disposed outwardly of the burner but inwardly of the surrounding walls of the duct structure for directing air into and through the burner. The laterally spaced converging plates define three air passageways through the duct structure, two outer air passageways between the respective plates and the surrounding walls of the duct structure and a third intermediate air passageway between the two plates with the intermediate air passageway being aligned with the burner. A preprogrammed heater control unit continuously monitors temperature, airflow and the flame about the burner and at the same time controls the temperature of the heated air being expelled from the heated air makeup unit.