What temperature should I set my thermostat in winter and summer?

There is no single right number, but there is a well-tested starting point. Dominion Energy suggests 68°F or lower in winter and 78°F or higher in summer, and, for extended time away, 62°F to 65°F in winter and 80°F to 83°F in summer.^[1] Start there, adjust a degree at a time for comfort, and let the thermostat do the rest on a schedule.

The settings matter because the bill is large. ENERGY STAR says almost half of the average American household's energy bill goes to heating and cooling, more than $900 a year.^[3]

Winter settings

For the hours you are home and awake, the Department of Energy suggested setting the thermostat to around 68°F to 70°F while you are awake, and lower while you are asleep or away.^[2] How much lower is where the savings are. The same guidance estimated savings of as much as 10% a year on heating and cooling for turning the thermostat back 7°F to 10°F for eight hours a day from its normal setting.^[2]

A practical winter week might look like this:

• Morning, home: 68°F.
• Workday, empty house: a setback, warming up shortly before people come home. Dominion's range for time away is 62°F to 65°F;^[1] the Department of Energy's 10% estimate assumes 7°F to 10°F below normal, which is 58°F to 61°F from a 68°F start.^[2] The deeper setback saves more; pick the one your household is comfortable with.
• Evening, home: 68°F.
• Night: the same setback, or whatever lets everyone sleep well.

Summer settings

For cooling, the Department of Energy's advice was to set the thermostat as high as is comfortable when you are home and need cooling, and warmer than normal when you are away, and to keep it low enough to ensure humidity control if needed.^[2] If the house feels clammy at 78°F, a degree lower may be the better trade than running fans and still feeling damp.

One habit wastes money every summer. Setting it colder than normal when you turn the air conditioner on will not cool the house any faster; it only runs longer and overshoots.^[2] Set the number you actually want and let the system get there.

Why setbacks save money

It can seem as if the system works harder to recover after a setback. In practice the house loses heat to the outdoors more slowly when it is cooler, so the longer it sits at the lower setting, the less energy it loses in total.^[2] The same works in reverse in summer: a warmer house gains heat more slowly.

A programmable or smart thermostat makes the schedule automatic, so nobody has to remember. How to set one up is in how to program a thermostat to save money.

Heat pumps are the exception in winter

If your home heats with a heat pump, the winter rule is different. The Department of Energy warned that setting back a heat pump in heating mode can make it run inefficiently and cancel the savings, and a moderate setting is the most cost-effective practice.^[2] Trane notes that the thermostat will trigger auxiliary heat if you raise the heating temperature by more than 3 to 4 degrees.^[5] So hold a moderate, steady setting, or use a programmable thermostat made for heat pumps: these typically use special algorithms to minimize the use of backup electric resistance heat.^[2]

Leave emergency heat alone in normal use. Trane says it should only be used in a true emergency, when the heat pump has failed and it is very cold outside.^[5] More on running one through the cold months is in how to keep a heat pump running well in winter.

Make sure the thermostat reads the room

The best setting is wasted if the thermostat is fooled. It should sit on an interior wall away from direct sunlight, drafts, doorways, skylights and windows, with furniture clear of it.^[2] Check it against a separate thermometer now and then. If the room is consistently more than 2°F to 3°F away from the setting, Carrier recommends having the thermostat and system checked.^[4]

Stop and call a pro if

• The house cannot reach your setpoint in normal weather, or the system runs almost nonstop. See why an HVAC system runs all the time.
• The thermostat reads more than a few degrees off a separate thermometer and recalibrating does not fix it.
• A heat pump shows auxiliary or emergency heat for long stretches when it is not very cold.
• The thermostat stops calling for heat or cooling at all. Start with why a thermostat is not turning on the heat.

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