What this calculator does
A heat pump does not make heat, it moves it, which is why it can deliver more heat energy than the electrical energy it consumes. The ratio is the coefficient of performance, and a seasonal COP of 3.2 means every kilowatt hour of electricity delivers 3.2 kilowatt hours of heat.
That is the whole argument, and it is also where the comparison with gas gets interesting. Electricity usually costs several times more per kilowatt hour than gas, so the heat pump only wins if its COP beats that price ratio. Work out where the line sits and the question stops being ideological.
The formula
Electricity used is heat needed ÷ COP. Gas used is heat needed ÷ boiler efficiency, since a boiler delivers less heat than the fuel contains. Resistance heating has a COP of exactly 1, so it uses as much electricity as the heat it produces. Setting the heat pump cost equal to the gas cost and solving gives the break-even COP, electricity price × boiler efficiency ÷ gas price, which depends on prices alone and not on how much heat you need.
| Term | Meaning |
|---|---|
| COP | Heat delivered per unit of electricity consumed. Instantaneous COP varies with outside temperature. |
| Seasonal COP | The average across a whole heating season, which is the figure to use here. Often called SCOP. |
| Boiler efficiency | The share of the gas energy that becomes useful heat. Condensing boilers reach the high 80s or low 90s in practice. |
| Resistance heating | Panel heaters and electric elements. COP of 1, and always the most expensive electric option. |
The inputs explained
| Field | What to enter |
|---|---|
| Heat needed per year (kWh) | Heat energy the house needs in a year, in kilowatt hours of heat rather than of fuel. If you only know your gas bill, multiply the gas used by the boiler efficiency. |
| Heat pump seasonal COP | The seasonal figure, not the headline one. Manufacturers quote COP at mild conditions, and a cold climate pulls the seasonal average well below it. |
| Electricity price ($/kWh) | Your electricity price. If the heat pump runs mostly off-peak or on solar, use that lower rate instead of the flat one. |
| Gas price ($/kWh) | Gas price per kilowatt hour. Bills are often in other units, so convert first. |
| Gas boiler efficiency (%) | Boiler efficiency as a percentage. An old non-condensing boiler may be nearer 70 than 90. |
When to use it
Deciding whether to replace a working gas boiler
The saving against gas is the number that matters, and on the default figures it is $428 a year. Compare that with the installation cost to get a payback, and remember the COP you should use is the seasonal one for your climate.
Replacing resistance heating
This is the easy case. A heat pump at COP 3.2 costs a third of what panel heaters cost for the same heat, saving $2,475 a year on these figures. There is almost no scenario where resistance heating wins.
Checking the break-even in your market
Enter your own electricity and gas prices and read the break-even COP. If it comes out above what your climate can deliver seasonally, gas is genuinely cheaper to run where you are, and that is worth knowing before committing.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
What COP do you need to beat gas?
Only the seasonal COP changes.
| Seasonal COP | Heat pump cost per year | Saving against gas | Electricity it uses |
|---|---|---|---|
| 1.00 | $3,600.00 | −$2,047.06 | 12,000 kWh |
| 1.50 | $2,400.00 | −$847.06 | 8,000 kWh |
| 2.00 | $1,800.00 | −$247.06 | 6,000 kWh |
| 2.32 | $1,551.72 | $1.22 | 5,172 kWh |
| 3.00 | $1,200.00 | $352.94 | 4,000 kWh |
| 4.00 | $900.00 | $652.94 | 3,000 kWh |
| 5.00 | $720.00 | $832.94 | 2,400 kWh |
How do energy prices move the break-even?
Only the electricity price changes.
| Electricity price | Heat pump cost per year | Saving against gas | COP needed to match gas |
|---|---|---|---|
| $0.15 | $562.50 | $990.44 | 1.16 |
| $0.20 | $750.00 | $802.94 | 1.55 |
| $0.30 | $1,125.00 | $427.94 | 2.32 |
| $0.40 | $1,500.00 | $52.94 | 3.09 |
| $0.50 | $1,875.00 | −$322.06 | 3.86 |
Questions
Is COP the same as the number on the brochure?
Usually not. Brochure COP is measured at a mild outdoor temperature. What matters for a yearly bill is the seasonal figure, often written SCOP, which averages across cold weather too and is always lower.
Why is resistance heating treated as COP 1?
Because an electric element converts essentially all the electricity into heat and no more. It cannot exceed 1, which is exactly what a heat pump does by moving heat rather than making it.
Does this cover hot water as well as space heating?
Only if you include the hot water energy in the heat figure. Hot water usually runs at a lower COP than space heating because it needs a higher output temperature.
What about carbon rather than cost?
A different question with a different answer, and it depends entirely on how your grid generates electricity. A heat pump on a clean grid beats gas on emissions even where it loses on cost.
How do I size the unit itself?
That is a capacity question rather than a running cost one. The furnace size calculator estimates heating capacity from floor area, climate and insulation level.
For sizing rather than running cost, see furnace size, and for the fabric side insulation upgrade payback. Running costs for a single appliance are on electricity running cost.