Programmable electronic thermostat with means for enabling economical recovery

A programmable electronic thermostat is provided for controlling operation of a multistage heating apparatus comprising a heat pump and auxiliary heat. A salient feature is a program which provides for economical recovery from a setback temperature. The program includes logic which determines, at the beginning of the recovery time, whether any or all of the auxiliary stages will be temporarily locked out and thus prevented from being energized. This determination is based on a characteristic which is dependent upon the heating demand that is presently being placed on the heating apparatus. The program also includes logic which determines, near the end of the recovery time, whether any or all of the locked stages are to be unlocked. This determination is based on the magnitude of the difference between the temperature existing at the time of determination and the temperature desired at the end of the recovery time.