Does Turning the Heat Down at Night Save Money?

Day 70°F, night 62°F: about 7 percent less heating on a cold night.

You have probably heard both versions: turning the heat down at night saves money, and turning it down costs more because the furnace has to "catch up" in the morning. The first one is right. A cooler house loses heat more slowly, and the furnace never has to pay back more than the house lost. Set it back 8 degrees for 8 hours and a gas furnace burns about 7 percent less on a cold night. Own a heat pump? Read the part about backup heat before you touch the schedule.

Why a cooler house is a cheaper house

A house leaks heat all the time, through walls, windows, the roof, and every little gap. How fast it leaks depends on one thing: the difference between inside and outside. Drop the inside from 70 to 62 on a 30 degree night and the gap shrinks from 40 degrees to 32, so the leak slows by a fifth.

Think of a bucket with a hole in it. The higher you keep the water, the faster it runs out, and the more you have to pour in. Let the level drop a bit overnight and you pour in less. In the morning you top it back up, but you only replace what leaked, and less leaked because the level was lower.

That is the whole trick. The furnace does run longer in the morning to warm the house back up, and that is exactly the heat it did not have to supply during the night. There is no penalty on top. Every hour the house sits cooler is an hour of slower leaking.

One catch. A house does not drop 8 degrees the moment the thermostat changes. Heavy, well insulated homes might only fall 4 or 5 degrees by morning, so they save a bit less than the simple math says. The saving is still real, just smaller.

What to set, and what to leave alone

Program a setback, do not do it by hand. A programmable or smart thermostat drops the temperature after bedtime and brings it back before the alarm, so nobody wakes up cold and nobody forgets. ENERGY STAR puts the typical saving from a certified smart thermostat at about 8 percent of heating and cooling costs, roughly 50 dollars a year, and closer to 100 dollars if the house is empty most of the day.

Start with the temperature you keep during the day. Each degree lower there saves more than a night setback, because it applies all 24 hours. A sweater and 68 beats 72 with a setback.

Set the morning recovery to start 30 to 60 minutes before you get up. Start it too late and you will be tempted to crank the dial. Cranking to 78 does not heat the house faster; the furnace only has one speed, so a high setting just overshoots and wastes the gain.

If you have a heat pump, keep the setback small, 2 to 4 degrees, or skip it. A big morning recovery makes most heat pumps switch on their electric backup strips, which cost two to three times more per degree than the heat pump itself. The Department of Energy says it plainly: do not set back a heat pump's thermostat if it makes the backup heat come on.

The most common version of this mistake I see: a homeowner installs a smart thermostat on a heat pump, copies a furnace schedule with a 10 degree night setback, and the winter bill goes up. The thermostat was calling for backup heat every morning at 6. Trimming the setback to 3 degrees fixed it.

When to call a pro

If your heat pump thermostat has an "aux" or "emergency heat" light that comes on most mornings, or your winter bills jumped after a thermostat change, have a technician check the backup heat settings and the outdoor sensor. That lockout setting is a five minute fix for someone with the manual, and it can be the difference between a heat pump that saves money and one that does not.

Go deeper: the setback arithmetic

Steady-state heat loss from a house is Q = UA × (T_in − T_out), where UA is the whole-house conductance. Take a 2,000 sq ft (186 m2) house with UA = 500 BTU/h·°F (264 W/K). At 70 °F inside and 30 °F (−1 °C) outside it loses 20,000 BTU/h (5.9 kW), or 480,000 BTU (141 kWh) a day.

Setting back 8 °F (4.4 K) for 8 hours lowers the driving difference from 40 to 32 °F for a third of the day. If the house dropped instantly, the saving would be 500 × 8 × 8 = 32,000 BTU (9.4 kWh), 6.7 percent of that day's heat. Through a 90 percent AFUE furnace that is 0.36 therms of gas. At the EIA residential average for March 2026, 16.16 dollars per thousand cubic feet, about 1.56 dollars per therm, the night is worth about 55 cents. On milder nights the same 8 °F is a larger share of a smaller heating bill, so the percentage rises but the dollars fall; the coldest weeks are where the setback earns the most.

The "catch-up" objection fails on energy balance: the morning recovery replaces exactly the heat the envelope lost while cool, which is by construction less than it would have lost warm. What the instant model overstates is the size of the drop. A heavy, well insulated house with a time constant of 24 hours or more falls only 3 or 4 °F in 8 hours, so the real saving lands nearer 3 to 4 percent. Light, leaky houses drop faster and save closer to the full figure.

Heat pumps change the cost side, not the physics. Recovery from a deep setback asks for capacity the compressor may not have at low outdoor temperature, and most thermostats respond by staging on electric resistance backup at a COP of 1.0 against a heat pump COP of 2 to 3. One hour of 10 kW strip heat costs more than the night saved. Thermostats with heat pump logic, adaptive recovery, and an auxiliary lockout avoid this; a 2 to 4 °F setback usually stays inside the compressor's capacity.

Indoor temperature through a 24 hour day, 30 °F outside.
The flat line holds 70 °F all day. The dipped line drops toward 62 °F after 10 pm and recovers before 6 am. The shaded area between them is the reduced indoor-outdoor difference, which is the heat the furnace did not have to supply: about 7 percent of the day's total if the house cools all the way, less if it cools slowly.

Sources

• ENERGY STAR, smart thermostat FAQ: certified smart thermostats save about 8 percent of heating and cooling bills, about 50 dollars a year on average
• ENERGY STAR, low- to no-cost tips: about 100 dollars a year if the home is unoccupied much of the day
• US Department of Energy, Energy Saver, operating and maintaining your heat pump: do not set back the thermostat if it causes the backup heating to come on
• Purdue Extension AE-94, home heating: about 3 percent change in annual fuel use per degree of thermostat setting
• US EIA, natural gas delivered to residential consumers, 16.16 dollars per thousand cubic feet, March 2026
• US EIA FAQ, heat content of natural gas, about 1,037 Btu per cubic foot