Turning the heat down while you are away usually reduces energy use, but shutting it off completely is not always wise. Outdoor climate, frozen-pipe risk, humidity, and heating-system type determine how far the setpoint should drop.
Lowering the setpoint reduces heat loss
The smaller the temperature difference between indoors and outdoors, the more slowly the house loses heat. That is why a reasonable setback over several hours can save energy without letting the home become extremely cold.
Do not put pipes or vulnerable occupants at risk
During freezing weather, maintaining a minimum indoor temperature helps protect pipes, especially in exterior walls or poorly insulated spaces. Pets, plants, older adults, and some materials may also set a practical lower limit.
Heat pumps may need a different setback strategy
A large setback can cause some heat-pump systems to bring on expensive auxiliary heat during recovery. If you have a heat pump, use a compatible thermostat and follow the setback strategy recommended for that system.
Long absences require more than a thermostat setting
For multi-day absences, consider frozen-pipe risk, alarms, water supply, and emergency access in addition to thermostat settings. Remote temperature monitoring can reveal a heating failure before it becomes property damage.
Sources
- U.S. Department of Energy — Thermostats — Thermostat use, temperature setbacks, and heating and cooling energy savings.