What the animation shows
The animation and the step-by-step video above use your numbers. Here is the same walkthrough written out for the default example.
What you enter
- How do you know your heating need?: From my past gas use.
- Past annual gas use for heating: 800 therms. From utility bills. Exclude water heating and cooking if possible.
- Efficiency of that old furnace (AFUE): 80 %.
- New furnace AFUE: 95 %.
- Heat pump HSPF2: 7.8. From the AHRI rating. HSPF2 is a seasonal average for a standard climate; colder climates see lower real efficiency.
- Electricity rate: 0.17 $/kWh. Find this on your utility bill: total charges ÷ kWh used gives an all-in rate.
- Natural gas rate: 1.4 $/therm.
What happens, step by step
- Both houses get the heat your old 80% furnace made from 800 therms.
- Heat pulled from outdoor air means buying only 8,205 kWh of electricity.
- The furnace burns 674 therms, and 5% of that heat goes up the flue.
- At your prices the furnace saves $451.71 a year.
The answer: heat pump yearly cost is $1,394.87.
How it’s calculated
- Delivered heat = past gas use × old AFUE (or the demand you enter)
- Heat pump seasonal COP = HSPF2 ÷ 3.412
- Heat pump kWh = heat ÷ COP; furnace therms = heat ÷ AFUE
- Cost = energy × your rate
Worked example
800 therms of past gas use in an 80% furnace; compare a 95% furnace and an HSPF2 7.8 heat pump at $0.17/kWh and $1.40/therm.
Inputs
- How do you know your heating need?
- From my past gas use
- Past annual gas use for heating
- 800 therms
- Efficiency of that old furnace (AFUE)
- 80 %
- Annual heat demand (delivered)
- 50 MMBtu
- New furnace AFUE
- 95 %
- Heat pump HSPF2
- 7.8
- Electricity rate
- 0.17 $/kWh
- Natural gas rate
- 1.4 $/therm
Results
- Heat pump yearly cost
- $1,394.87
- Gas furnace yearly cost
- $943.16
- Difference (furnace − heat pump)
- $-451.71
- Heat pump electricity
- 8,205 kWh
- Furnace gas
- 674 therms
- Heat pump seasonal COP used
- 2.29
- Gas price where costs are equal
- 2.07 $/therm
Assumptions and limits
- HSPF2 represents average seasonal performance for a standard climate region; actual COP varies with outdoor temperature.
- Rates are constant all year.
Verify the result against the applicable local code, adopted code edition, manufacturer instructions and project requirements. See our methodology.
Questions
Is a heat pump cheaper to run than a gas furnace?
It depends on the ratio of your electricity to gas price and the heat pump’s cold-weather efficiency. Enter your own rates — the break-even gas price output shows where the two costs match.
What is HSPF2?
Heating Seasonal Performance Factor (2023 test procedure): seasonal BTUs of heat per watt-hour of electricity. Dividing by 3.412 gives an average COP.