in the summer, keep it at 78°F. In the winter, set your thermostat at 68°F in the daytime and 55°F at night. Remember that water heaters work most efficiently between 120°F and 140°F. In your refrigerator, set the temperature at about 37°F and adjust the freezer to operate at about 3°F.

 

Source: SimpleLivingInstitute.org