How this calculator works
Your yearly heating gas use tells us how much heat your home actually needs: therms × 100,000 Btu × furnace efficiency. A heat pump has to deliver the same heat. Its seasonal efficiency (COP) is its HSPF2 rating ÷ 3.412, so the electricity it needs is the heat divided by COP and by 3,412 Btu per kWh.
The break-even electricity price is where both cost the same; below it, the heat pump wins. If you would disconnect gas entirely, the fixed monthly gas charge is counted as a saving too.
Assumptions and tips
- Heating only — air conditioning savings from a heat pump are not included.
- Prices stay flat for the year.
Worked example
Using the default values in the calculator above:
| Input | Value |
|---|---|
| Gas used for heating per year | 600 therms |
| Furnace efficiency (AFUE) | 90 % |
| Gas price | 1.5 $/therm |
| Heat pump HSPF2 rating | 8.1 |
| Electricity price | 0.17 $/kWh |
| Fixed gas charge you’d stop paying | 0 $/month |
| Result | Value |
|---|---|
| Gas furnace saves | $233/yr |
| Gas furnace heating cost | $900/yr |
| Heat pump heating cost | $1,133/yr |
| Break-even electricity price | $0.135/kWh |
| Heat pump electricity use | 6,667 kWh/yr |
| Seasonal efficiency (COP) | 2.37 |
| Heat delivered | 54 million Btu |
Step by step:
- Heat needed = 600 therms × 100,000 × 90% = 54 million Btu
- Heat pump COP = 8.1 ÷ 3.412 = 2.37
- Electricity = 54,000,000 ÷ (2.37 × 3,412) = 6,667 kWh
- Heat pump cost = 6,667 × $0.17 = $1,133; gas cost = 600 × $1.5 = $900
Break-even electricity price by gas price
With a 90% AFUE furnace and an HSPF2 8.1 heat pump — below this electricity price, the heat pump costs less to run.
| Gas price | Break-even electricity price |
|---|---|
| $0.90 per therm | $0.081/kWh |
| $1.20 per therm | $0.108/kWh |
| $1.50 per therm | $0.135/kWh |
| $1.80 per therm | $0.162/kWh |
| $2.10 per therm | $0.189/kWh |
| $2.50 per therm | $0.225/kWh |
Common mistakes to avoid
- Using your total gas bill — water heating, cooking and dryers are not part of heating.
- Comparing a heat pump’s rated efficiency at 47°F with real winter performance; use the seasonal HSPF2.
Frequently asked questions
Is a heat pump cheaper than a gas furnace?
It depends on your gas and electricity prices. At $1.50 per therm, a 90% furnace and an HSPF2 8.1 heat pump cost the same to run at about 13.5¢ per kWh; a cold-climate HSPF2 10 model breaks even near 16.7¢.
How do I find how much gas I use for heating?
Look at a year of gas bills. Subtract a typical summer month (water heating and cooking) from each winter month and add up the differences.