Abstract: An off-peak electric heat storage and discharge device includes variably sized thermal media material contained in a rock box. A calrod-type heating element is located in and in direct thermal contact with the thermal media material. Air flow can move from a fan upwardly through a duct, through slots formed in the duct into the rock box, and through the thermal media material. Air flow can also move from the fan through a bypass duct. Heated air and cold air can be mixed in proper proportions by a rotatable damper movable between a position closing off all cold, bypass air and a position closing off all heated air. The damper falling to shut off the flow of heated air in the event of an actuator failure. All electric controls and the fan are contained in a vertical control chamber designed to convectively convey heat during static conditions. The thermostat for the device is located at the lowest point possible in the vertical control chamber and below a point which could be affected by convective air flow.