Calculate SimplyHow to use
Start with the worked example to understand the inputs, then replace every relevant value with your own figures. Use one currency and consistent units throughout. Add or remove rows where offered; irrelevant conditional fields are disabled and excluded. Select Calculate after editing. Review negative values and any “not determined” result rather than assuming every scenario must be profitable. Download a text summary or print the page for your records.
Formula and assumptions
Enter temperature bands using manufacturer COP and capacity data together with an independently assessed home heat load and hours per band. The heat pump supplies the smaller of load and capacity; gas or electric resistance supplies the shortfall. Divide delivered heat by COP for electricity, and by furnace efficiency and 29.300111 kWh per therm for gas. Seasonal COP is heat-weighted through total heat divided by total input. A thermal balance point is interpolated only when capacity crosses load once in your bands. HSPF2 is not treated as a temperature-specific COP. Emissions require user-supplied factors.
heat = load × hours; HP heat = min(load, capacity) × hours; HP electricity = HP heat / COP; gas therms = gas heat / (29.300111 × furnace efficiency)
Worked example
Example only: replace rates with your own figures.
Inputs
- Electricity rate per kWh: 0.2
- Gas rate per therm: 1.5
- Gas furnace efficiency: 90 %
- Backup heat for capacity shortfall: gas
- Include emissions estimates: No
- Electricity emissions factor: 0 kg/kWh
- Gas emissions factor: 0 kg/therm
| Outdoor temperature | Hours in temperature band | Heating load in this band | Heat pump COP in this band | Heat pump capacity in this band |
|---|---|---|---|---|
| -10 | 600 | 8 | 2 | 6 |
| 0 | 1000 | 5 | 3 | 6 |
| 10 | 500 | 2 | 4 | 7 |
- Heat pump plus backup cost: 811.592 USD
- Gas-only heating cost: 614.332 USD
- Seasonal savings: -197.26 USD
- Heat pump seasonal COP: 2.58296
- Cost break-even COP: 3.51601
- Interpolated thermal balance point: -3.33333 °C
Frequently asked questions
Are the example rates current market prices?
No. Example inputs demonstrate arithmetic, not live prices, tax rules, salary surveys or sponsor benchmarks. Enter a dated quote, bill, manufacturer specification or verified fee schedule that applies to your situation. Compare a conservative and an optimistic scenario separately.
Why is a result not determined?
Some calculations have no meaningful value when a denominator is zero, savings are non-positive, a target cannot be reached or your data do not bracket an intersection. The tool leaves that result undetermined instead of displaying infinity or inventing a recommendation. Check the method and your inputs.
Sources
Sources explain the underlying concepts, not an endorsement of this website or its results. Method review: 20 October 2026.