Abstract: The invention consists of an electrical heating apparatus which provides for controlled fuel substitution in a heating system, particularly a forced-air central heating system. The electrical heater assembly is mounted in the system and a device is provided to select electricity as the heating fuel when off-peak periods in electricity demand occur. Since the cost of producing electrical energy during these off-peak periods is well known to be lower than during peak period times, the user of the invention will realize savings in total heating fuel costs through the substitution of electrical energy for the primary fuel, such as oil, wherever the off-peak price of electricity is sufficiently lower than the energy-equivalent price of the primary fuel. Where fossil fuels, principally oil, are used as the primary heating fuel, the invention will further act to conserve increasingly scarce and increasingly costly fuel supplies.