Thermostat Setback Savings Calculator

How the calculation works

Your heating bill depends on how much warmer you keep the inside than the outside, and for how long. Lower the inside temperature for part of the day and you shrink that gap, so the house loses less heat. The calculator uses a simple degree-hour method.

Average gap      = normal indoor setting − average winter outdoor temperature
Setback used     = smaller of (degrees turned down, average gap)
Share saved      = (setback used × hours per day) ÷ (24 × average gap)   (capped at 100%)
Yearly savings   = share saved × yearly heating cost

In plain words: the “degree hours” you remove each day, divided by the degree hours your home normally needs each day, gives the share of heating you avoid.

The method assumes heat loss rises in step with the indoor-outdoor gap, that the house cools to the setback temperature quickly, and that warming back up costs no more than the heat saved. These are simplifications. Real homes take time to cool, so actual savings can be lower than the full setback suggests.

The result lines up with official guidance. DOE’s Energy Saver guide says turning the thermostat down 7°F to 10°F for 8 hours a day can save as much as 10% a year on heating and cooling.

Worked example

The default home keeps 68°F, has an average heating-season temperature outside of 38°F, and spends $1,200 a year on heat.

1. The setback is 8°F for 8 hours a day, such as overnight.
2. The share of heating cost saved works out to about 9%.
3. On a $1,200 heating bill, that is about $107 a year.

A second example

A colder home keeps 70°F through a winter that averages 30°F outside, and spends $1,800 a year on heat. The household sets back only 5°F, but for 10 hours a day while everyone is at work and school.

• Share of heating cost saved: about 5%
• Yearly savings: about $94

A smaller setback saves a smaller share. In this colder climate, the same degrees are also a smaller part of a bigger heating load, though the larger bill keeps the dollar savings close.

What your result means

The percent is the share of your heating cost the setback could save. The dollar figure applies that share to the heating cost you entered. If you enter your whole energy bill instead of just heating, the dollars will be too high.

Every hour and every degree adds up, so a setback you will actually keep is worth more than an ambitious one you will drop. A programmable or smart thermostat makes it automatic. Our smart thermostat savings guide explains settings, wiring and utility programs.

Climate, equipment and other factors that change the answer

Climate. Space heating and air conditioning together made up 52% of household energy use in 2020, according to EIA’s survey data. In mild climates, a setback is a bigger share of a smaller bill. In cold climates, it is a smaller share of a bigger bill.

Equipment. Furnaces and boilers handle setbacks well. Heat pumps are the exception, as above; our heat pump cost and savings guide explains how backup heat works. If your system is slow to warm the house, schedule the recovery to start earlier so rooms are warm when you need them.

House tightness. A setback trims a share of whatever heating your home needs. Sealing leaks and adding insulation shrink that need in the first place, around the clock. See our guide on how to lower your energy bill for the best upgrades in order.

Cooling. The same idea works in summer: set the thermostat higher while you are out. This calculator covers heating only.

To find out what your heating costs per unit of heat across fuels, try the heating fuel cost comparison calculator. If your energy bills are a big share of your income, the energy burden calculator puts them in context.

Common mistakes

• Entering your total energy bill instead of the heating part.
• Using the coldest night’s temperature instead of the heating-season average.
• Counting hours when the setback is set but the house has not cooled yet.
• Using large setbacks with a heat pump that switches to backup heat on recovery.
• Expecting the same percent in summer; cooling savings follow different math.

Limits of this calculator

This is a simplified degree-hour estimate. It does not model how slowly your house cools and warms, sun through windows, heat from people and appliances, or how your heating system behaves at different loads. It overstates savings for long setbacks in tight, well-insulated homes that never reach the lower temperature. This is an educational estimate, not advice.