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Thermostat Setback Savings Calculator

Enter your annual heating cost, setback degrees and setback hours to see the savings.

How it is calculated

The tool applies a rule of thumb of about 1 % of heating cost saved for each degree Fahrenheit of setback held for 8 hours a day: saving % = setback °F × (hours ÷ 8). The saving in money is annual cost × saving % ÷ 100, and the new cost is the annual cost minus that saving. The percentage is capped at 50 %. The setback must be above 0 and at most 20 °F, and the hours above 0 and at most 24; values outside those ranges return no result. The setback is in °F, so a 1 °C drop is 1.8 °F. This is a rough average: climate, insulation and how the boiler recovers change the real figure.

Worked example

Annual heating cost of 1,500, thermostat lowered by 5 °F for 10 hours a day. Saving percentage: 5 × (10 ÷ 8) = 5 × 1.25 = 6.25 %, shown as 6.3%. Annual saving: 1,500 × 6.25 ÷ 100 = $93.75. New annual cost: 1,500 − 93.75 = $1,406.25. Setting back the same 5 °F for only 8 hours would save 5 %, or $75.00.

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Common mistakes

  • Entering the setback in °C. The field is °F, so a 3 °C drop must be entered as about 5.4, not 3.
  • Entering the new temperature (for example 64) instead of the number of degrees lowered. The tool rejects anything above 20, but a value like 15 would claim a 15 % saving.
  • Using the monthly or winter-only bill as the annual cost. The result is a percentage of whatever you type, so use the full year's heating cost.
  • Counting the hours the heating is off, not the hours the thermostat is set back. If the heating is also unused for weeks, the saving is overstated.
  • Expecting a bigger saving by adding more degrees. The percentage is capped at 50 %, and deep setbacks lose some of the saving to the recovery period.

About this calculator

The calculator is built on the well-known heating rule of thumb popularized by U.S. Department of Energy field studies: for roughly every degree Fahrenheit you set the thermostat back, you save about 1% of your heating cost per 8 hours of daily setback — a rule this calculator applies to the annual heating cost you enter, scaling linearly with both the degrees and the daily hours. The relationship is close to linear over the modest setbacks most households actually use — a few degrees overnight or while the house is empty during the workday — because heat loss through walls, windows, and roof scales with the difference between indoor and outdoor temperature, so a lower indoor target means slower, cheaper heat loss.

Programmable and smart thermostats made this kind of scheduled setback routine, and homeowners use a savings estimate like this one to decide whether a nightly or daytime setback is worth the temporary chill, and to set realistic expectations before buying a smart thermostat marketed on energy savings. The actual percentage saved varies with climate, insulation quality, and how efficiently the furnace responds to recovery, but the 1%-per-degree-per-8-hours figure remains the standard back-of-envelope estimate used by energy advisors.

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