A heater and/or demister device D for installing in a heater and/or demister circuit of a vehicle. The device D is provided with a fan 7 for producing a flow of warm air from a flow of ambient air and a flow of compressed hot air taken from an engine of the vehicle. The device comprises a cylindrical outer body 9 surrounding the fan 7 and an impeller 3, the impeller 3 being fed with the flow of compressed hot air and driving the fan 7.