Additional electric heater for vehicles

The unit (1) has a positive temperature co-efficient (PTC) heating element (4) for heating air flowing through the unit, and a control unit (2) for adjusting amount of heat in the heating element. A temperature determination unit (3) determines cold air temperature from a weighted combination of a vehicle interior and vehicle exterior temperature. The control unit adjusts the amount of heat as a function of the determined cold temperature such that temperature of the air discharged from the unit is varied based on vehicle speed. Independent claims are also included for the following: (1) a motor vehicle seat comprising a backrest and an air duct (2) a method for controlling an electric auxiliary heating unit for a motor vehicle.