Understanding your result
The headline is the cheapest fuel for your house and what a season costs with it, with its cost per million BTU and the season’s heat in the sub-line. The bars rank all seven fuels by season cost, and the stats show the three cheapest. The table gives every fuel’s season cost, the quantity of fuel it would use (therms, gallons, kWh, tons or cords), the price and efficiency you entered and the cost per million BTU delivered, which is the figure to remember: it does not depend on your house, only on your prices and equipment.
The notes state the ratio between the dearest and the cheapest fuel and the break-even electricity price for a heat pump against gas at your gas price and furnace efficiency. If your tariff is below it, the heat pump is cheaper to run; if above, gas is, and the margin tells you how much the equipment and installation costs have to weigh in the decision.
The season’s heat comes either from the design load and your climate zone’s degree days or from a figure you enter; the degree-day fuel estimate does that step in more detail with your own degree days, and the furnace size calculator gives the load. For a per-unit view without the house, the fuel cost per million BTU calculator ranks fuels alone, and the heat pump versus gas furnace calculator goes deeper into the two front-runners with cold-weather COP and backup heat.
How we calculate this
The season’s heat uses the degree-day method: the house’s heat loss per degree, from the design load and the design temperature, multiplied by the hours in a day and the heating degree days of the zone (base 65 °F), with the ASHRAE correction factor of 0.65 that accounts for internal and solar gains and part-load behaviour. Zone degree days are typical NOAA normals, rounded, listed on the BTU per square foot table. The energy content of each fuel is the EIA figure on the fuel energy content page: 100,000 BTU per therm, 91,452 per gallon of propane, 138,500 per gallon of heating oil, 3,412 per kWh, 16.5 million per ton of pellets and about 20 million per cord of air-dried hardwood.
Efficiency divides the delivered heat to get the fuel burned: AFUE for furnaces and boilers, 100% for resistance heat, the seasonal COP for a heat pump, and typical combustion efficiencies for pellet and wood stoves.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Natural gas | $1.50 per therm, 95% AFUE | EIA residential natural gas price, 2025 (about $15 per thousand cubic feet); condensing furnace |
| Propane | $2.70 per gallon, 95% AFUE | EIA residential propane price, 2024–25 heating season |
| Heating oil | $3.70 per gallon, 85% AFUE | EIA residential heating oil price, 2024–25 heating season; typical oil furnace |
| Electricity | $0.17 per kWh | EIA residential average, 2025 |
| Heat pump | COP 2.8 (entered as 280%) | A seasonal COP typical of an HSPF2 9 to 10 air-source unit in a cool climate |
| Pellets | $300 per ton, 80% | Typical bagged retail price; EPA-certified pellet stove efficiency |
| Cordwood | $300 per cord, 70% | Typical delivered price (varies $200 to $450); EPA-certified wood stove efficiency |
| Energy content | EIA: 100,000 BTU/therm, 91,452/gal propane, 138,500/gal oil, 3,412/kWh, 16.5 MMBtu/ton pellets, 20 MMBtu/cord | US Energy Information Administration |
| Degree-day correction | 0.65 | ASHRAE Handbook, Fundamentals, degree-day method (0.6 to 0.8) |
Assumptions last reviewed October 7, 2026.
The calculator does not include equipment, installation or maintenance costs, the backup resistance heat that a heat pump uses on the coldest days (which raises its effective cost in cold climates), fixed monthly charges on a gas account, or the labour of a wood stove. Prices are national averages that vary two-fold between states. The guide to comparing fuels per million BTU explains the method, and the guide to heat pumps in cold climates covers why a heat pump’s winter COP is lower than its rating.
Two worked examples
A zone 5 house at national average prices
Design heat load 60,000 BTU/hr in climate zone 5 (0 °F design, about 6,300 heating degree days), default 2025 prices and efficiencies.
- Heat loss per degree: 60,000 ÷ 70 = 857 BTU/hr per °F
- Season heat: 857 × 24 × 6,300 × 0.65 = 84.2 million BTU
- Natural gas at 95%: $15.79 per million BTU → $1,330 (887 therms)
- Heat pump at COP 2.8: $17.79 → $1,499 (8,817 kWh)
- Cordwood $1,805; pellets $1,915; propane $2,618 (970 gal); oil $2,648 (716 gal); electric resistance $4,197 (24,688 kWh)
Gas wins by about $170 a year over the heat pump, and the break-even note says the heat pump would win below 15.1 cents per kWh. Electric resistance costs 3.2 times as much as gas, which is the arithmetic behind replacing electric baseboard with a heat pump in any climate.
A milder house with cheap electricity and dearer gas
45 million BTU of heat a season entered directly; gas $1.90 per therm, electricity $0.12 per kWh, heat pump COP 3.0, oil $4.10 per gallon, other defaults.
- Heat pump at COP 3.0: $11.72 per million BTU → $528 (4,396 kWh)
- Natural gas at 95%: $20.00 → $900 (474 therms)
- Cordwood $964; pellets $1,023; propane $1,398; oil $1,567; electric resistance $1,583
With 12-cent electricity and $1.90 gas the order flips and the heat pump saves $370 a year over gas. The break-even electricity price is 20.5 cents per kWh, so the heat pump has a wide margin here. Note that electric resistance at 12 cents is still nearly three times the heat pump’s cost, because the heat pump delivers three units of heat per unit of electricity.
Where to find your inputs
Design heat load. From the furnace size calculator or a Manual J report. If you know last year’s fuel use instead, multiply it by the energy content and the efficiency to get the heat delivered, and use the annual mode.
Prices. Gas from the bill as the total divided by therms (or ccf × 1.037), including delivery charges; propane and oil from the delivery ticket; electricity as the total bill divided by kWh; pellets and wood from the supplier.
Efficiencies. AFUE from the yellow label or nameplate; the heat pump’s seasonal COP as HSPF2 ÷ 3.412 (or the manufacturer’s seasonal figure); stove efficiencies from the EPA certification label.
Degree days. Set by the climate zone here; the degree-day calculator takes your own figure from NOAA or a utility.
Common mistakes
- Comparing fuel prices without the energy content. $3.70 oil against $1.50 gas is not a 2.5-to-1 ratio; a gallon of oil holds 1.385 therms, so it is 1.8 to 1 before efficiency.
- Forgetting the efficiency. An 80% furnace needs a quarter more fuel than a 100%-efficient one; a heat pump needs a third of the electricity of a resistance heater.
- Using the energy-only rate. Delivery charges and taxes often double the headline rate for gas and electricity; use the all-in figure.
- Entering a heat pump’s rated COP for a cold climate. Rated COP is at 47 °F; the seasonal figure in zone 5 or 6 is 2.5 to 3.
- Ignoring fixed charges. A gas account carries a monthly fee of $10 to $30 even when the furnace is off; add it when gas is the only gas appliance.
- Reading the ranking as a buying decision. Running cost is one part; equipment, installation and lifespan are on the upgrade payback calculator.
Questions people ask
- What is the cheapest way to heat a house?
- At 2025 US average prices, natural gas in a condensing furnace, at about $16 per million BTU delivered, then an air-source heat pump at a seasonal COP of 2.8, about $18. Cordwood and pellets follow at $21 to $23 if you pay retail, then propane and heating oil at about $31, and electric resistance heat last at about $50. Local prices move the order. Where electricity is cheap or gas is unavailable, the heat pump wins; where gas is $1 per therm, nothing beats it.
- How much does it cost to heat a 2,000 square foot house for a winter?
- For a house with a 60,000 BTU per hour design load in a cool climate (zone 5, about 6,300 heating degree days), the season's heat is about 84 million BTU. At 2025 average prices that is roughly $1,330 with natural gas at 95% AFUE, $1,500 with a heat pump at COP 2.8, $2,600 with propane or oil and $4,200 with electric baseboard. A mixed-climate house of the same size uses about 60% of that; a very cold one about 150%.
- What is cost per million BTU and why use it?
- The price of a fuel divided by its energy content, scaled to a million BTU and divided by the efficiency of the equipment, so that it describes heat delivered to the rooms rather than fuel bought. Natural gas at $1.50 per therm (100,000 BTU) in a 95% furnace is $1.50 ÷ 100,000 × 1,000,000 ÷ 0.95 = $15.79 per million BTU. Because every fuel is reduced to the same unit, the figures can be compared directly and multiplied by the house's annual heat to get the season's bill.
- How is a heat pump's efficiency entered?
- As the seasonal coefficient of performance multiplied by 100, so a COP of 2.8 is entered as 280%. The COP is the heat delivered divided by the electricity used over the whole season; HSPF2 ÷ 3.412 is a fair estimate (an HSPF2 of 8.5 is a COP of about 2.5), and cold climates lower it while mild ones raise it. Ground-source heat pumps run at COPs of 3 to 4.5 and are entered the same way.
- When does a heat pump beat a gas furnace?
- When the electricity price in dollars per kWh is below the gas cost per million BTU multiplied by the COP and by 3,412 ÷ 1,000,000. At $1.50 per therm and 95% AFUE, gas is $15.79 per million BTU, and a COP 2.8 heat pump beats it below 15.1 cents per kWh; at a COP of 3.2 the threshold is 17.2 cents. The calculator prints this break-even for your prices. In most of the Pacific Northwest and the South the heat pump wins; in New England at 25 cents per kWh gas usually does.
- Why is heating oil quoted per gallon but gas per therm?
- Habit and metering. Oil and propane are delivered by the gallon, gas is metered by volume and billed by energy (a therm, or sometimes a ccf of about 1.037 therms), electricity by the kilowatt-hour, pellets by the ton and firewood by the cord. The energy in each unit is on the fuel energy content page, and the calculator does the conversions so you only have to type the price from your bill or delivery ticket.