 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.For example, during cooling season, a programmable thermostat used in a home may be set to allow the temperature in the house to rise during the workday when no one will be at home.