Use a cold-month gas bill, with any non-heating charges removed.
Quoted price after any rebates you already qualify for.
Heat pump seasonal COP ÷ your current system's efficiency. A COP of 3.0 against a 90% efficient furnace gives 3.3. Use ~4.0 against an older 75% furnace, or ~3.2 against a 95% condensing model.
Estimated Monthly Savings
Payback Period
595 months
Heat Pump Running Cost
Annual Savings
Electricity Needed
How this calculation works
A dollar amount on a gas bill can't be compared to an electricity rate directly, so the bill is first converted back into energy, then re-priced as electricity:
Walking the numbers above: a $180.00 bill at $1.50 per therm buys 120.0 therms, which is 3516 kWh of purchased energy. A heat pump with an efficiency advantage of 3.3 delivers the same useful heat from 1065 kWh of electricity, costing $159.82 at $0.15 per kWh — a saving of $20.18 a month, paying back the install cost in about 49.5 years.
A long payback here is usually the correct answer rather than a mistake. At the US averages loaded above — around $1.50 per therm of gas against $0.15 per kWh of electricity — a therm of gas energy costs about 5.1 cents per kWh, so a heat pump at an advantage of 3.3 lands within a cent of the gas it replaces. The running-cost case gets decisive when you enter what you actually pay: propane and heating oil typically run around twice the cost per unit of heat, and replacing electric resistance heating cuts the bill by the full efficiency advantage.
The efficiency advantage is what the result really hinges on, and it is a seasonal average rather than a nameplate figure: a heat pump is far more efficient at 45°F than at 5°F, so a unit rated 4.0 in mild weather may average closer to 2.5 across a cold winter. Two things this estimate leaves out, both in the heat pump's favour — the same unit usually replaces your air conditioning in summer, and rebates often cut the install cost well below the sticker price.
Common questions
- Why does this calculator show such a long payback?
- Because against cheap natural gas that is usually the honest answer. At around $1.50 per therm, gas energy costs about 5 cents per kWh, and a heat pump with an efficiency advantage of 3.3 at 15 cents per kWh lands within a cent of it. The running-cost saving is small, so the install cost takes a long time to recover. The case changes sharply if you heat with propane, oil or electric resistance.
- What efficiency advantage figure should I use?
- Divide the heat pump’s seasonal COP by your current system’s efficiency. A COP of 3.0 against a 90 percent efficient furnace gives 3.3. Use around 4.0 against an older 75 percent furnace, or about 3.2 against a 95 percent condensing model. Use a seasonal average rather than a nameplate figure, since a heat pump is far more efficient at 45F than at 5F.
- What does this calculation leave out?
- Three things, and they mostly favour the heat pump. The same unit usually replaces your air conditioning in summer, which this does not credit. Rebates and tax credits often cut the install cost well below the sticker price. Against that, a very cold climate may need backup resistance heat on the coldest days, which adds cost the simple model does not capture.