Heating system for a vehicle

The system has a blower (24) for producing a hot air flow for feeding into a vehicle interior, a heater (22) with a heat exchanger arrangement (26) for heating the hot air flow, a mixer arrangement (20) for setting an external/recirculated air ratio of air for feeding to the heat exchanger arrangement, a sensor arrangement (60) for producing an output related to external temperature and an arrangement (42,46) for controlling the mixer arrangement to set the ratio based on the sensor arrangement output.