Abstract: An aircraft cabin air heater system for a multiengine aircraft having a cabin and a nose duct communicating therewith includes an electric resistance air heater unit positioned in the cabin and provided with air ducts leading from the cabin to the air heater unit and back to the cabin. A fan associated with the air ducts and heater unit recirculates air from the cabin through the air ducts and heater for heating the air. The air ducts are connected to the nose duct and are arranged to permit sufficient outside air to enter the cabin through the nose duct to maintain the oxygen level sufficient for passenger comfort while limiting the amount of outside air to that which will permit the air heater unit to maintain the cabin temperature at a comfortable level. An alternator driven by one of the engines provides electrical power to the air heater unit and serves as an auxiliary back-up electrical power for the aircraft in case the aircraft's main electrical power supply fails.