Thermostat Setback Calculator
See how much of the season’s heating or cooling energy a setback trims, from how many degrees and how many hours a day. Based on the DOE rule of about 1% per degree per 8 hours.
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Data: DOE thermostat setback guidance (about 1% per degree per 8 hours, up to about 10% for a 7 to 10°F setback) · Updated September 2026
How setbacks reduce energy use
Less temperature gap, less heat loss
A house loses heat in proportion to the gap between inside and outside. Every degree you set back for part of the day shrinks that gap for those hours, and the furnace or AC runs less. DOE puts it at about 1% of seasonal energy per degree per 8 hours, which is what this tool applies.
The recovery myth
Heating the house back up does not undo the setback for a furnace, boiler or central AC. The house lost less heat while it was cooler, and recovery only replaces that smaller loss. The exception is a heat pump with electric backup strips, which can kick in during a fast recovery.
Why the number is capped
The rule stops scaling once the house has coasted to its balance with the outdoors, so this tool caps the reduction at 20%. Milder climates see a bigger share than severe ones, and a drafty house sees more than a tight one.
Common questions
About 1% of the season’s heating energy for every degree held for 8 hours a day, per DOE. An 8°F setback for 8 hours is about 8%; the same setback overnight and during the workday roughly doubles it.
DOE suggests 68°F while you are home and awake, lower while asleep or away. In summer, 78°F when home and higher when away. The size of the setback matters more than the exact number.
Only a small one. A deep setback makes a heat pump call for its electric backup strips during recovery, which can erase the gain. Keep setbacks to 2 to 4°F or use a thermostat with a heat pump recovery mode that warms the house up slowly.
No. A furnace or boiler runs at one output, so setting 80°F to reach 70°F just overshoots. Set the temperature you want and let it get there.
It makes the setback automatic, which is what makes the reduction real. A smart thermostat that learns when you leave and come back does the same without programming, and the heat pump models handle recovery correctly.
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