Guide · 8 min read · free tool
Heat Pump Savings: COP, Gas Price, and a Bill That Is Not a Slogan
Sep 16, 2026 · Zelpura Editorial · All guides
Heat pumps are marketed as if they replace a fuel bill with a rounding error. What they actually do is move heat with electricity, and the number of heat units you get per unit of electricity is the coefficient of performance, the COP. A COP of 3 means you get about three units of heat for one unit of electricity, which is why a heat pump can beat gas even though electricity looks expensive per kilowatt-hour on the bill. It can also lose to gas if the COP collapses in the cold and the electric rate is high. This calculator exists so that sentence has inputs instead of a team jersey.
The page asks for annual heating need in kilowatt-hours, a gas price, an electric price, and a COP. Heating need is the hard one. It is not your current gas bill, because the bill is price times quantity, and you need the quantity. If you can get therms or kilowatt-hours of heat from a year of bills, start there. If you only have dollars, you will smuggle the old rate into the need and then compare it to a new rate, which double-counts the price. Convert last year's fuel into energy, then let this page apply the new prices. That is the whole trick, and it is the step most kitchen-table comparisons skip.
COP is not a single sticker for all weather. A mild-climate COP and a January COP are different machines wearing the same logo. If your winters are serious, do not type the best number on the brochure. Type a seasonal number you are willing to defend, or run the page twice: once at the optimistic COP and once at the ugly one. The ugly one is the one that should decide whether the swap is a financial project or a comfort project. Comfort projects are allowed. They should not be required to pretend they cash-flow in a week of polar air if they do not.
People forget the rest of the house. A heat pump dropped into a leaky, barely insulated building is being asked to manufacture comfort that insulation would have kept. Sometimes the first dollar belongs in the attic, and the heat pump can be smaller afterward. Run the insulation calculator and the AC sizing page with the new assumption before you let a contractor size the equipment to the house as it leaks today. Oversizing a heat pump has cousins in the short-cycling problem you already know from air conditioning. Bigger is not automatically kinder to the bill or to humidity in cooling season, and many of these machines do both jobs.
Backup heat is the line that wrecks a pretty model. If the system falls back to electric resistance strips on the coldest nights, those hours are COP 1, which is ordinary electric heat, which is often the expensive way to stay warm. Ask how often the quote assumes strips will run. If the answer is 'almost never' and you live where 'almost never' is two weeks, redo the COP. Fuel switching can also change the fixed monthly charges on the gas bill. If you still pay a gas customer charge because the stove remains, you did not delete the entire gas bill. Delete only the part you actually delete.
This is a fuel-cost sketch, not a load calculation, not a refrigerant design, and not a rebate determination. Incentives can change the cash without changing the physics. A rebate you do not qualify for is not cash. Electrical panel upgrades, line sets, and a pad that has to be poured are part of the installed cost even though they are not fields here. Get them into the quote as lines, not as 'we'll see.' Compare two quotes on the same heating need. If one assumed half the load, it is not a cheaper heat pump. It is a different house.
After the first heating season, compare energy use to the need you typed. If you used much more electricity than the COP implied, either the COP was a story, the house needed more heat, or the strips ran. The bill will not label those causes in friendly English. The installer should. Keep the proposal. Circle the COP. A year from now you want to be arguing about a circled number, not about a memory of a kitchen table. Heat pumps can be an excellent trade. They are a trade. Type the prices you pay, not the prices in a national slideshow, and let a weak COP be allowed to lose.
Check three things on the quote before you celebrate a savings year: the seasonal COP they will actually stand behind in your climate, whether resistance backup is in the model, and whether the gas customer charge remains. Then run this page at that COP and at a COP half a point worse. If the worse case still looks fine, you have a project. If only the brochure case looks fine, you have a brochure. Insulation, air sealing, and a right-sized machine beat a hero COP taped to a leaky lid. Do the boring work first if the dollars say so. The machine will still be for sale next month.
Related: AC BTU · Insulation · Home battery · All 93 tools