Heating and cooling losses from a building (or any other container) y allowing the temperature difference to be reduced at times when the reduced amount of heating or cooling would not be objectionable.
Heating and cooling losses from a building (or any other container) become greater as the difference in temperature increases. A programmable thermostat allows reduction of these losses by allowing the temperature difference to be reduced at times when the reduced amount of heating or cooling would not be objectionable.