How this calculator works
The U.S. Department of Energy says you can save as much as 10% a year on heating and cooling by turning the thermostat back 7–10°F for 8 hours a day from its normal setting. That works out to roughly 1% for each degree held for 8 hours a day. The calculator scales that rule of thumb by your setback, hours and days, and caps it at 15%.
The saving is real because a house loses heat faster the warmer it is inside — a cooler house for part of the day loses less, and the furnace makes up less.
Assumptions and tips
- A rule of thumb: actual savings are larger in cold climates and leaky houses, and smaller in mild climates.
- Use only the heating (or cooling) part of your energy bills.
Worked example
Using the default values in the calculator above:
| Input | Value |
|---|---|
| Yearly heating (or cooling) cost | $1,200 |
| Setback | 8 °F |
| Hours per day at the setback | 8 h |
| Days per week | 7 |
| Result | Value |
|---|---|
| Estimated savings per year | $96 |
| Savings | 8 % of cost |
| Per month (12 months) | $8.00 |
| Degree-hours of setback per week | 448 °F·h |
Step by step:
- Savings ≈ 8°F × (8 h ÷ 8) × (7 ÷ 7 days) = 8%
- $1,200 × 8% = $96 a year
Yearly savings on a $1,200 heating bill
Every night, 8 hours — calculated with this tool.
| Setback | Estimated savings per year |
|---|---|
| 2°F | $24 |
| 4°F | $48 |
| 6°F | $72 |
| 8°F | $96 |
| 10°F | $120 |
Common mistakes to avoid
- Cranking the thermostat up to warm the house faster — furnaces heat at the same rate whatever the setting.
- Deep setbacks with a heat pump that switches to expensive backup heat to recover.
Frequently asked questions
How much do I save by turning the thermostat down at night?
About 1% of your heating cost per degree for an 8-hour setback — 8°F overnight on a $1,200 heating bill saves around $96 a year.
What temperature should I set in winter?
DOE suggests about 68–70°F while you are awake, and lower while you sleep or are away.
Does it cost more to reheat the house?
No. The energy to reheat is less than what the house would have lost staying warm, except with heat pumps that switch to strip heat.
Sources
Built and reviewed by Anirban Kundu, Creator & Editor · M.Sc Physics, 20 years teaching science