Abstract: An off-peak, electric, central air heating system for buildings incorporating a heat storage material that is used to store heat generated electrically during off-peak electrical power periods and to deliver heat on demand. The heat storage material is an alkaline metal or alkaline earth metal salt such as Na.sub.2 SO.sub.4, NaCl, CaCl.sub.2 and KCl individually or in combination with one another. Generation of heat during the off-peak electrical power periods is automatically controlled by an electronic time clock and time delay circuitry, and by selective variable temperature control. The heating unit is constructed with a casing having an inner jacket and an outer jacket with an air space between the two jackets. The storage material is surrounded by the inner jacket and the air space provides insulation as well as an air passage between the two jackets.