Abstract: A system for heating the passenger compartment of an automotive vehicle has a hot water heater receiving heat from a vehicle engine arranged in series with a self-regulating electrical resistance heater of positive temperature coefficient of resistivity, has a power source for energizing the electrical resistance heater, and has a fan for directing air in heat-transfer relation to the hot water heater and to the electrical resistance heater in sequence to provide a heated air output to the passenger compartment. Fan speed is controlled to regulate the volume of air directed in heat-transfer relation to the heaters so that the electrical resistance heater is promptly and consistently capable of heating that volume of air to at least a selected minimum temperature such as 100.degree. F. as the heated air output is furnished to the passenger compartment, thereby to give a vehicle passenger an immediate and continuing sensation of comfort beginning very promptly after engine start-up even on a very cold day.