The comparison comes down to one price
Both machines have to put the same heat into the house, so the fair comparison is the cost of one million Btu of heat. A furnace needs 10 therms of gas for each million Btu, divided by its AFUE as a fraction. A heat pump needs 1,000,000 ÷ HSPF2 watt-hours, which is 1,000 ÷ HSPF2 kWh.
Set the two costs equal and you get the break-even electricity price: gas price per therm × HSPF2 ÷ AFUE in percent. If the electricity price you pay is below that number, the heat pump costs less to run. If it is above, the furnace does.
For example, with a 95 percent furnace and a heat pump rated 7.8 HSPF2, gas at $1.20 per therm breaks even at $0.099 per kWh. Gas at $2.00 breaks even at $0.164.
Break-even electricity price by gas price
The table assumes a 95 percent AFUE furnace. The three heat pump columns use the ENERGY STAR minimums: 7.8 HSPF2 for split systems, and 8.1 and 8.5 for its cold climate tier (ducted and non-ducted split systems). A heat pump with a higher rating has a higher break-even price, so it stays cheaper at higher electricity prices.
| Gas price per therm | HSPF2 7.8 | HSPF2 8.1 | HSPF2 8.5 |
|---|---|---|---|
| $0.80 | $0.066 | $0.068 | $0.072 |
| $1.20 | $0.099 | $0.102 | $0.107 |
| $1.60 | $0.131 | $0.136 | $0.143 |
| $2.00 | $0.164 | $0.171 | $0.179 |
Where a heat pump looks best (2024 prices)
Using 2024 average residential prices from EIA, these are the five states where the electricity price is lowest compared with the break-even price for a 7.8 HSPF2 heat pump against a 95 percent furnace. At 7.8 HSPF2, the average electricity price is at or below break-even in 6 of the 51 places in the data.
These are statewide averages that include fixed charges, so a household can land on either side. Use them to see where you start, then enter the rates on your own bills.
| State | Gas per therm | Electricity per kWh | Break-even at HSPF2 7.8 |
|---|---|---|---|
| Florida | $2.45 | $0.141 | $0.201 |
| Louisiana | $1.58 | $0.117 | $0.130 |
| Arizona | $1.97 | $0.149 | $0.162 |
| Arkansas | $1.55 | $0.123 | $0.127 |
| Missouri | $1.63 | $0.129 | $0.133 |
Where a heat pump looks worst
These are the five states where electricity is the most expensive compared with gas. A heat pump needs a much higher HSPF2, or a lower electricity rate than the state average, to come out ahead.
| State | Gas per therm | Electricity per kWh | Break-even at HSPF2 7.8 |
|---|---|---|---|
| Alaska | $1.13 | $0.248 | $0.093 |
| Michigan | $1.04 | $0.193 | $0.085 |
| Connecticut | $1.62 | $0.288 | $0.133 |
| Wisconsin | $0.98 | $0.172 | $0.080 |
| California | $1.85 | $0.320 | $0.152 |
What AFUE and HSPF2 do and do not tell you
ENERGY STAR describes AFUE as, in general, the percentage of the heat in the incoming fuel that is converted to space heat instead of being lost. The calculator reads a 95 percent AFUE as 95 percent of the gas energy reaching the house as heat.
HSPF2 is the heat a heat pump supplies over a heating season, in Btu, divided by the electricity it uses, in watt-hours. ENERGY STAR defines it for a single reference climate, region IV. Dividing by 3.412 turns it into a seasonal COP: 7.8 HSPF2 is a COP of 2.29, and 8.5 is 2.49. That division is our arithmetic on EIA's 3,412 Btu per kWh.
Because the rating comes from one reference climate, a home in a colder place can use more electricity than its HSPF2 suggests. The calculator does not guess a correction. It gives you the break-even HSPF2 so you can judge the margin yourself.
Cold weather and backup heat
ENERGY STAR certification requires third-party verified performance at low temperatures, with air-source heat pumps tested down to 5°F. Its cold climate tier asks for a COP of at least 1.75 at 5°F, on top of the higher HSPF2 levels in the table above.
ENERGY STAR also says a cold climate heat pump keeps working below 5°F, and that pairing it with a back-up energy source heats the home most efficiently when temperatures are lower still. If a home keeps a gas furnace as the backup, the calculator above compares full replacement, not a mix of the two.
What the running-cost comparison leaves out
- Equipment and installation. Prices, ducts, electrical work and gas line work differ for every home. Get written quotes for both options.
- Cooling. A heat pump can also cool the house. If you would otherwise replace your air conditioner too, that belongs in the comparison. Our AC BTU calculator shows what size a room air conditioner needs.
- Rebates and tax credits. They depend on your location, income and the date, and change often. This site does not estimate them.
- Price changes. The state prices are annual averages for one year. Gas and electricity prices move, and not together.