When leaving the house, it is appropriate to set the thermostat 4 degrees Fahrenheit warmer in the summer and 4 degrees cooler in the winter. A larger differential can create humidity in the home during the summer.
Raising or lowering the thermostat too much during an absence also causes an electric heating or cooling unit to work excessively hard when the temperature is set back to normal. Gas furnaces can be set up to 8 degrees lower in the winter because they heat more efficiently. The U.S. Department of Energy estimates that during the winter, for every degree the thermostat is turned down for at least eight hours, up to 1 percent is saved on the heating bill.