There is provided a heater for a room heating system. The heater comprises a heating element and a housing for the heating element. The housing comprises opposed first and second ends and a longitudinally extending sidewall there between. The heating element is mounted to and extends longitudinally from the first end. A thermal distribution fluid inlet to the housing and outlet from the housing are provided. The housing contains the thermal distribution fluid as it follows a flow path from the inlet to the outlet. One of the inlet and the outlet extends through the sidewall of the housing. The heater is a backup heater in a room heating system mostly powered by a heat pump.
