Understanding your result
The headline says which system is cheaper to run and by how much a season, with the two season costs and the break-even electricity price in the sub-line. The bars put the two costs side by side. The table gives the season’s heat, the heat pump’s effective COP after backup, its electricity, the furnace’s fuel, both season costs, both costs per million BTU, the difference, and the break-even price of electricity and of the furnace fuel.
The break-even rows are the most useful part. The break-even electricity price tells you the tariff below which the heat pump wins; if your utility offers a heat pump rate or a time-of-use rate, compare it with this figure. The break-even fuel price tells you how far gas, propane or oil would have to rise for the heat pump to catch up.
The effective COP row shows what backup heat does. A 10% share of strip heat looks small but takes a COP of 2.8 down to 2.37, because those BTU cost almost three times as much. The heat pump size calculator finds the balance point that decides how much backup a given unit needs, the heating cost by fuel calculator ranks all seven fuels for the same house, and the heat pump installation cost calculator prices the equipment.
How we calculate this
The season heat uses the degree-day method with the ASHRAE correction factor of 0.65, from the zone’s typical design temperature and heating degree days on the BTU per square foot table. The effective COP is a weighted harmonic mean: the strips deliver their share of the heat at a COP of 1, the compressor delivers the rest at its seasonal COP, and the electricity for each is added. Fuel energy contents and default prices are on the fuel energy content and cost page.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Heat pump seasonal COP | 2.8 | Typical air-source unit of HSPF2 9 to 10 in a cool climate |
| Backup share | 10% | Typical for a standard heat pump in zones 5 to 6; 0 to 5% mild climates or cold-climate models |
| Furnace AFUE | 95% | Condensing gas furnace |
| Prices | $0.17/kWh, $1.50/therm, $2.70/gal propane, $3.70/gal oil | EIA residential averages, 2025 |
| Season heat | Degree-day method, correction 0.65 | ASHRAE Handbook, Fundamentals |
| Zone data | Design temperature and HDD by zone | Typical NOAA normals and ASHRAE design data, rounded |
Assumptions last reviewed October 8, 2026.
The calculator uses one seasonal COP, where a real heat pump’s COP rises above 3.5 in mild weather and falls below 2 near its balance point, and it does not model defrost energy, the furnace blower (about 5 to 7% on top of the gas cost), or the cooling a heat pump also provides. The guide to heat pumps in cold climates covers balance points and dual-fuel switchover, and the guide to degree days explains the season-heat estimate.
Two worked examples
A gas-heated house in zone 5 at average prices
60,000 BTU/hr design load in zone 5 (0 °F design, 6,300 HDD), heat pump COP 2.8 with 10% backup, 95% gas furnace at $1.50 per therm, electricity at $0.17.
- Season heat: 60,000 ÷ 70 × 24 × 6,300 × 0.65 = 84.2 million BTU
- Effective COP: 1 ÷ (0.9 ÷ 2.8 + 0.1) = 2.37
- Heat pump: 10,404 kWh × $0.17 = $1,769
- Furnace: 887 therms × $1.50 = $1,330
- Furnace saves $439; break-even at 12.8 cents per kWh
At these prices gas wins in Chicago. A cold-climate heat pump with 3% backup would raise the effective COP to about 2.65 and cut the gap to about $230; a heat pump tariff of 12 cents would flip the result.
A propane house in a milder climate
50 million BTU per season, heat pump COP 3.2 with 3% backup, 95% propane furnace at $2.70 per gallon, electricity at $0.14.
- Effective COP: 1 ÷ (0.97 ÷ 3.2 + 0.03) = 3.0
- Heat pump: 4,881 kWh × $0.14 = $683
- Furnace: 576 gallons × $2.70 = $1,554
- Heat pump saves $870 a season; break-even at 31.8 cents per kWh
Propane is about twice the cost of gas per BTU, so the heat pump wins easily and would keep winning even if electricity doubled. Houses on propane, oil or resistance heat are where heat pumps pay back fastest.
Where to find your inputs
Heating need. The design load from the furnace size calculator or a Manual J; or last winter’s fuel use multiplied by its energy content and the furnace’s efficiency, entered as annual heat.
COP. HSPF2 ÷ 3.412 from the heat pump’s label; ground-source units list COP directly.
Backup share. From a smart thermostat’s auxiliary heat hours, or the typical ranges in the field’s hint.
Prices. All-in prices from your bills, including delivery.
Common mistakes
- Using the rated COP without backup. In a cold climate strips can take the season’s COP down by 15% or more.
- Comparing without the furnace’s efficiency. An 80% furnace burns a fifth more gas than a 96% one.
- Forgetting the fixed gas charge. Removing gas entirely saves the monthly service fee too.
- Using an energy-only electricity rate. Delivery charges often double it.
- Ignoring dual-fuel. A furnace below the break-even temperature gets the best of both.
- Deciding on running cost alone. Equipment, the AC replacement and comfort count too.
Questions people ask
- Is a heat pump cheaper to run than a gas furnace?
- It depends on the electricity-to-gas price ratio and the climate. At 2025 US averages, 17 cents per kWh and $1.50 per therm, a heat pump at a seasonal COP of 2.8 costs about $17.80 per million BTU against $15.80 for a 95% gas furnace, so gas wins slightly before backup heat; with 10% strip heat the heat pump's effective COP drops to 2.37 and gas wins by about a quarter. With electricity at 12 to 14 cents, or gas above $2 a therm, the heat pump wins.
- What is the break-even electricity price for a heat pump?
- The price at which a season on the heat pump costs exactly what a season on the furnace does. For a zone 5 house with a 95% gas furnace at $1.50 per therm and a heat pump at COP 2.8 with 10% backup, it is about 12.8 cents per kWh. Without backup it is about 15.1 cents. Each 0.1 rise in COP raises it by about half a cent; each 10 cents on the gas price raises it by about a cent.
- How much does a heat pump save over propane or oil?
- A lot, because propane and oil cost about $31 per million BTU delivered at 2025 average prices, roughly double gas. For a house needing 50 million BTU a season, a heat pump at COP 3.2 with 3% backup at 14 cents per kWh costs about $683, against about $1,554 for a 95% propane furnace, a saving of about $870 a year. Heat pumps pay back fastest in houses heated with propane, oil or electric resistance.
- How much heat comes from backup strips?
- It depends on the climate, the heat pump and its size. A standard heat pump sized for cooling in a cold climate (zones 5 to 6) may get 10 to 25% of its season's heat from strips; a cold-climate model, or any heat pump in a mild climate, 0 to 5%. A smart thermostat that reports auxiliary heat run time, or the balance point from the heat pump size calculator, gives a better figure than a guess.
- What is a dual-fuel system?
- A heat pump paired with a gas or propane furnace instead of electric strips. The heat pump heats down to a switchover temperature, typically 25 to 40 °F, chosen where the furnace becomes cheaper per BTU, and the furnace takes over below it. It combines the heat pump's low cost in mild weather with the furnace's capacity on the coldest days, and it is common where gas is cheap and winters are cold.
- Does this include the cost of the equipment?
- No, only the running cost. A heat pump also replaces the air conditioner, which matters when both the furnace and the AC are due for replacement; a furnace-only replacement is cheaper to install. Gas service also has a fixed monthly charge, $10 to $30, that disappears if gas is removed entirely. The upgrade payback and installation cost calculators handle the equipment side.