Thermostat Setback Savings Estimator
Turning the heat down while you sleep or are out reduces heat loss for those hours. Estimate the share of heating energy and money it can save.
Method reviewed October 26, 2026. Version 1.0.0. How it works
This is an estimate. It uses a simplified method and typical assumptions, all listed below. Use it to plan and to check quotes; equipment should be sized from a full room-by-room load calculation (ACCA Manual J) by a qualified professional.
Result
- Heating energy saved (upper estimate)
- 8.89%
- Yearly saving
- $107
A 8 °F setback for 8 hours a day saves up to about 8.9 % of heating energy at a 38 °F seasonal average.
- Public guidance from energy offices says setting back 7–10 °F for 8 hours a day can save as much as 10 % a year on heating and cooling. This estimate is an upper bound: it ignores the extra heat needed to warm the house back up and the heat stored in the structure.
- Heat pumps: deep setbacks can make the backup electric heat run during recovery, which can cancel the saving. Use a small setback or a thermostat designed for heat pumps.
Show the working
- Average indoor–outdoor difference without setback68 − 38 = 30 °F
- Fraction saved ≈ (hours × setback) ÷ (24 × difference)(8 × 8) ÷ (24 × 30) = 8.9 %
- Yearly saving = heating cost × fraction$1,200 × 0.089 = $106.67
The degree-hour method
A house loses heat in proportion to the difference between indoor and outdoor temperature. Over a heating season, the average difference is your set point minus the average outdoor temperature. Lowering the set point by S degrees for H hours a day cuts the season’s degree-hours by about (H × S) ÷ (24 × average difference).
For example, 68 °F with a 38 °F season average is a 30 °F difference; an 8 °F setback for 8 hours saves up to about 8.9 %. Energy offices give similar guidance: as much as 10 % a year for a 7–10 °F setback for 8 hours a day. Milder climates save a larger percentage because the average difference is smaller.
Why the real saving is lower
The estimate is an upper bound. The building’s structure and furniture store heat, so the indoor temperature does not drop instantly, and the heating system must run harder to warm the house back up. Both trim the saving.
Heat pumps are a special case: a deep setback can make the backup electric heat run during recovery, which can wipe out the saving. Use a small setback, or a thermostat designed for heat pumps. Slow radiant-floor systems also respond poorly to setbacks.
Worked example
These are the example values the calculator opens with, and the result the engine calculates for them.
Inputs
- Normal heating set point
- 68 °F
- Setback (degrees lower)
- 8 °F
- Hours per day at the lower setting
- 8 h
- Average outdoor temperature over the heating season
- 38 °F
- Yearly heating cost (optional)
- 1,200 $
Result
- Heating energy saved (upper estimate)
- 8.89 %
- Yearly saving
- $107
A 8 °F setback for 8 hours a day saves up to about 8.9 % of heating energy at a 38 °F seasonal average.
Assumptions
- Heat loss is proportional to the indoor–outdoor temperature difference (Q = U·A·ΔT, including air leakage), so lowering the indoor temperature for some hours cuts the season’s degree-hours by the same share.
- Internal and solar gains are ignored; they make the real percentage somewhat higher in mild weather but do not change the method.
Limitations
- Upper estimate: recovery heating and heat stored in the building reduce the real saving.
- Not valid for heat pumps with resistance backup during recovery, or for slow radiant-floor systems.
- Heating only; cooling loads are driven partly by sun and internal gains, so this method does not transfer to summer set-ups.
Frequently asked questions
Does the furnace use more energy warming the house back up than it saved?
No — for furnaces and boilers the house loses less heat while it is cooler, so there is a net saving. The recovery only makes it smaller than the simple estimate.
What average outdoor temperature should I use?
The average of daily mean temperatures over the months you heat. NOAA climate normals for your nearest station give monthly means.
Does this work for cooling?
Raising the set point in summer also saves energy, but cooling loads come partly from sun and internal heat, so this heating method does not estimate it.
Sources
- Heat Loss from Buildings — The Engineering ToolBox. Conduction heat loss Q = U·A·ΔT with U = 1/ΣR.
- Thermostats — Maryland Energy Administration. Households 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; programmable setback is generally not recommended for heat pumps in heating mode, where a moderate steady setting is most cost-effective.
- Units and calculators explained: Degree-days — U.S. Energy Information Administration. Degree days compare the daily mean temperature with a 65 °F base; heating degree days accumulate when the mean is below 65 °F.
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