Abstract: A radiantly heated furnace is provided with a heating arrangement capable of generating heat from two different sources of energy. The arrangement includes a thin-walled tube extending within the furnace which operates as a resistor when connected to a high current source of electrical energy to generate and radiate heat within the furnace. The thin-walled tube also acts to radiate heat into the furnace from hot burner gases injected therein by a fuel fired burner. The arrangement is so constructed that switching from the electric to the gas fire mode or vice versa can be swiftly effected without removal of electrical connections or burners.