The system has a main heater (12) with its fan (10) powered by gas from a gas supply carried with the caravan. A heating tube (14) from the heater leads to the space to be heated. At least one electrical resistive heating element (16) is mounted in the heating tube. The electrical resistive heating element is connected to a temp. switch mounted upstream. The system contains a manually operated gas flow override switch. The heating element can only be supplied with power when the fan is operating and has its own fan.
