Abstract: In a motorcar space heating system of the type having a heat pipe comprising a heat absorbing element for receiving heat from the exhaust gas of the motorcar engine and a heat discharging element for heating air flowing into a car interior space to be heated, the heat pipe is separated, at an intermediate heat exchanger installed in a working fluid passage connecting the heat absorbing and discharging elements, into a heat absorbing section and a heat discharging section. The working fluids within these two sections are therefore not intermingled with each other. A pipe extends from the intermediate heat exchanger so as to be communicative at one end thereof with the heat absorbing section. The other end of the pipe extends into a working fluid reservoir tank.

Abstract: A heat pipe provided with a vaporizable working fluid is utilized to transfer heat from exhaust gas flowing through the exhaust pipe of an engine driving a vehicle to air flowing through an air duct to an interior space to be heated in the vehicle. The heat pipe has a loop return pipe for returning condensed fluid to a heat absorption part of the heat pipe and a control valve in the return pipe for controlling the flow of returning fluid, the control valve being controllable manually or automatically by a temperature control system including a sensor in the air duct, a control circuit, and a solenoid valve actuator.