The heaters are used successfully by farmers and gardeners. Whether in well-ventilated stalls, equipment sheds, or greenhouses, their mobility makes them practical and universal. The heaters are delivered ready for plug assembly. They are ready for operation after connection to the 230-volt a.c. mains and to propane gas cylinder(s). For energy savings, the devices can be delivered in automatic design (PGT) with a room thermostat that is ready for plug assembly.