Abstract: A heater comprising a sealed container (4) having an internal partially evacuated cavity provided with at least one internal heating means (14), the cavity containing a working fluid, such as water, that vaporizes upon introduction of heat to the cavity from the heating means.

Abstract: A heater comprising a substantially vertical heatpipe in contact or fluid communication with at least one additional heatpipe that is extendable in a substantially horizontal direction therefrom, at least one of the heatpipes being at least partially evacuated and having an internal cavity for receiving a working fluid and at least one of the heatpipes being adapted to receive heat from an internal or external heat source.