What is the single biggest way to lower a heating bill?

Insulation and air sealing. On the model house, going from poor to good insulation cuts the gas season from $1,019.43 to $458.75, a saving of $560.68 every winter.

How much does a thermostat setback save?

About 1% per degree for 8 hours, up to 10% for a 7 to 10 degree setback, per the DOE. On the default house an 8 degree setback saves $59.84 and a 10 degree setback saves $74.80 a season.

Does lowering the thermostat at night damage the furnace?

No, for furnaces: a cooler house loses heat more slowly, and reheating costs less than the heat saved. Heat pumps are the exception, because deep setbacks can trigger expensive backup resistance heat.

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The heating ledger · Table No. 37

How to Lower Your Heating Bill

Ranked by dollars on the same house: insulation first, setback second, daytime temperature third, and the furnace throughout.

Filed October 25, 2026 · figures checked against 2026 sources

Ranked by dollars, not by vibes

Heating advice usually arrives as a list of tips with no prices attached, which makes it impossible to choose. This article ranks the moves by dollars saved on one house, the calculator's default: 1,800 square feet, moderate climate, gas heat at $1.35 per therm, thermostat at 68 degrees with an 8 degree setback for 8 hours, season cost $688.12. Every figure below comes from changing one input and holding the rest fixed, so the ranking is honest about what each move is worth on this house, and the calculator lets you rerun it on yours.

First: fix the envelope, worth $560.68

The biggest single move is insulation and air sealing. The same house with poor insulation costs $1,019.43 for the season; with average insulation it costs $688.12; with good insulation it costs $458.75. Going from poor to good saves $560.68 a season, more than every thermostat trick combined, and the saving repeats every winter for the life of the work. Going from average to good still saves $229.37 a season. Sealing is the unglamorous half of this: caulk, weatherstripping, and sealing the gaps where pipes and wires enter the house cost little and cut the drafts that force the furnace to run longer. Insulation without sealing leaves the holes; sealing without insulation leaves the walls cold. The pair is what moves a house between the model's rows.

The honest caveat is that envelope work costs money upfront, unlike thermostat changes, which are free. But the payback arithmetic is unusually kind: a house leaking from the poor row to the average row saves $331.31 a season, so even a four-figure sealing and insulation job pays back in a handful of winters, and then keeps paying. If your house is genuinely poor, meaning drafty rooms, cold walls, and a furnace that never seems to rest, start here and skip the gadget aisle.

Second: the night setback, worth $59.84 to $74.80

The Department of Energy says turning the thermostat back 7 to 10 degrees Fahrenheit for 8 hours a day can save as much as 10% a year on heating and cooling, about 1% per degree for 8 hours. On the default house, the pre-setback season is $747.95. An 8 degree setback for 8 hours saves 8%, or $59.84, bringing the season to $688.12. A 10 degree setback for 8 hours saves 10%, or $74.80, bringing it to $673.16. The mechanism is simple and often disbelieved: a cooler house loses heat to the outdoors more slowly, so the furnace runs less, and reheating costs less than the heat saved during the setback hours. The DOE addresses the objection directly, and the physics agrees.

Two qualifications matter. First, the setback only saves while it is actually held: a programmable thermostat that runs the schedule every night beats a manual habit that remembers three nights a week. Second, heat pumps are the exception. A deep setback on a heat pump can trigger backup resistance heat during recovery, which is the most expensive heat in the house, and can erase the saving. Heat-pump owners should keep setbacks to 2 or 3 degrees, or use a thermostat with adaptive recovery that warms the house gradually without calling for backup heat.

Third: the daytime setting, worth $82.57 for two degrees

Every degree above 68 costs about 3% on this model. Raise the daytime setting from 68 to 72 and the pre-setback season rises from $747.95 to $837.71; after the same 8 degree setback, the season is $770.69 instead of $688.12, a difference of $82.57 for two degrees of comfort. The reverse is equally true: dropping from 70 to 68 saves roughly 6% before setback, and it stacks with the setback saving rather than replacing it. Clothing, blankets, and a warm room to retreat to are not folk wisdom here; they are the cheap substitute for two degrees of whole-house heat.

The practical version of this advice is a schedule, not a sacrifice. Heat the house to comfort when people are home and awake, drop it when they sleep or leave, and let the thermostat do the remembering. The DOE's suggested winter setting is around 68 degrees while awake and lower while asleep or away, and that schedule is where the 10% figure comes from. A house held at 72 around the clock is paying for empty rooms and sleeping hours at full price.

The boxed insight. On the default house, insulation from poor to good is worth $560.68 a season, while the celebrated thermostat setback is worth $59.84. The setback is free and real, but it is the second move, not the first: fix the envelope, then optimize the schedule, and never buy a gadget before sealing a draft.

Fourth: heat only the rooms you use

Size scales the bill almost linearly in this model. At 1,200 square feet the gas season is $458.75; at 2,500 square feet it is $955.72, a difference of $496.97 for 1,300 square feet. Closing off a genuinely unused wing, shutting its vents, and letting it ride cooler through the winter is worth real money, with one warning: do not close so many vents that the furnace strains, and never let pipes freeze. A room you close should stay above freezing, and a house with water pipes in exterior walls needs more care than a house with interior plumbing. The saving is real, but frozen pipes erase a decade of it in one night.

Fifth: maintain the machine

A furnace that runs dirty runs longer. A clogged filter restricts airflow and forces longer cycles; a neglected burner wastes fuel up the flue. The model assumes 80% efficiency for a gas furnace, and a poorly maintained furnace can fall below that, silently adding a percentage to every month of the season. Annual service, a clean filter every month or two through the heating season, and clear vents are cheap insurance. They will not transform a bill the way insulation does, but they protect the efficiency every other saving assumes.

The order to do things in

Seal and insulate first, because $560.68 beats everything else and repeats every winter. Set the thermostat schedule second, because $59.84 to $74.80 is free and starts tonight. Drop the daytime setting a degree or two third, because $82.57 for two degrees stacks with the setback. Close unused rooms fourth, with the frozen-pipe warning attached. Maintain the furnace throughout, because every saving above assumes the machine runs at its rated efficiency. That order is the whole article: the expensive fix first, the free fixes next, the gadget last, if at all.

Saving on heating questions

What is the single biggest way to lower a heating bill?: Insulation and air sealing. On the model house, going from poor to good insulation cuts the gas season from $1,019.43 to $458.75, a saving of $560.68 every winter.
How much does a thermostat setback save?: About 1% per degree for 8 hours, up to 10% for a 7 to 10 degree setback, per the DOE. On the default house an 8 degree setback saves $59.84 and a 10 degree setback saves $74.80 a season.
Does lowering the thermostat at night damage the furnace?: No, for furnaces: a cooler house loses heat more slowly, and reheating costs less than the heat saved. Heat pumps are the exception, because deep setbacks can trigger expensive backup resistance heat.