Oil, Gas or Heat Pump: What a Winter Costs Now

Everybody in an old house keeps some version of the same record: the delivery slips in a kitchen drawer, or the online account with last January’s bill on it. In February, with the wind coming through the north side of the house, those numbers are the most interesting reading in the building. They are also the only figures in this story that belong to you, and they’ll tell you more than any general claim about heat pumps.

Most writing on this question reaches for a single savings figure. We won’t print one. The answer turns on four numbers that differ from house to house and move during the winter: what you pay for fuel, how efficiently the old system burns it, what you pay for electricity, and how efficiently a heat pump turns that electricity into heat in your particular house. Change any of them and the verdict can flip.

This winter, one of those numbers has moved a lot. The state’s weekly survey put retail heating oil at an average of $6.15 a gallon for the week of 11/02/26, against $3.63 a year earlier. A comparison run last winter is out of date, so here’s how to run this winter’s. We leave out what a system costs to install, because that’s a separate question, and we make no promise about payback.

How do you compare oil and a heat pump on the same scale?

Convert both to the cost of a million BTU of heat delivered into the house. It’s a clumsy unit but a fair one, because it strips out the difference between a gallon and a kilowatt-hour. You need only two formulas.

For oil: price per gallon x 1,000,000, divided by (138,500 x boiler efficiency). The 138,500 is EIA’s heat content for a gallon of heating oil.

For a heat pump: price per kWh x 1,000,000, divided by (3,412 x COP). One kilowatt-hour holds 3,412 BTU, and COP, the coefficient of performance, is how many units of heat the machine delivers for each unit of electricity it uses. A COP of 1 is a plain electric baseboard. A COP of 3 means three units of heat out for one unit paid for.

Put this week’s oil price into the first one, with an assumed boiler efficiency of 85 percent. Each gallon delivers 138,500 x 0.85, or 117,725 BTU. A million BTU takes about 8.49 gallons, and 8.49 x $6.15 comes to about $52.24. If your old boiler is closer to an assumed 75 percent, the same sum gives about $59.21. Nobody’s boiler has a sticker with its true running efficiency on it, so a recent combustion test, if the service technician left you one, is the better guide. Otherwise treat these as assumptions.

For electricity, we’ve assumed $0.30 per kWh. It isn’t a quote, though it sits close to EIA’s Massachusetts residential average of 30.19 cents for the year to date through August 2026. Your own figure is better: take a recent bill, divide the total dollars by the kilowatt-hours, and use that.

How much does a heat pump cost to run in Massachusetts compared with oil?

At these assumptions, a heat pump costs less to run than oil whenever its COP stays above about 1.7, and more when it falls below that. The break-even is simple to find. A heat pump at COP 1 needs 293 kWh per million BTU, which at an assumed $0.30 costs $87.92. Divide that by oil’s $52.24, and you reach a COP of 1.68.

Now run it for a whole season, on a house we’ve invented. Say a hypothetical house burned 600 gallons in a year, entirely on heat. That number is an example and isn’t typical of anything; use your own. At $6.15 that’s $3,690, though of course you’d never pay this week’s price for an entire winter. At an assumed 85 percent, those gallons delivered 600 x 117,725 BTU, or about 70.6 million BTU. Dividing by 3,412 gives 20,702 kWh of heat. Then divide by a seasonal COP:

The gap is sensitive to the things we assumed. At an assumed $0.25 per kWh, the break-even against $6.15 oil drops to a COP of about 1.4. At an assumed $0.35, it rises to about 2.0. And look at last year’s oil: at $3.63 a gallon, with the same 85 percent boiler and $0.30 power, a million BTU cost $30.83 and the break-even COP was about 2.85. Oil prices that moved that far in twelve months can move again, in either direction. We’d run the sum at more than one oil price before relying on it.

Oil prices that moved that far in twelve months can move again, in either direction.

If your boiler also makes your hot water, part of those gallons were never space heating. Summer deliveries give you a rough sense of how much, and a heat pump for the rooms won’t replace that use. The story on the water heater that stays behind covers what happens next.

What about natural gas and propane?

Gas is the harder comparison for a heat pump to win, and propane looks a lot like oil at this week’s price. The state survey has propane at $3.92 a gallon for the week of 11/02/26. EIA puts a gallon at 91,452 BTU. At an assumed 85 percent, that’s about $50.43 per million BTU delivered, and a break-even COP near 1.74 against $0.30 power.

For gas we went to EIA’s Massachusetts natural gas prices, which give a statewide residential average of $27.17 per thousand cubic feet for March 2026, the last month of last winter in the current table. Summer months in that table run higher and shouldn’t be used for a heating sum. At 1,036 BTU per cubic foot, that’s about $2.62 a therm, or $26.23 per million BTU in the fuel. With an assumed 85 percent system, it comes to about $30.85 delivered, and the break-even COP is about 2.85.

So on these assumptions a gas house has much less room than an oil house this winter, and the heat pump would need to run efficiently through the season to come out ahead. That doesn’t settle the matter, since a gas house may want cooling, may have a failing boiler, or may pay a different gas rate from the state average. Your own bill gives the true number: total dollars divided by therms, including delivery. Divide that by your efficiency, then multiply by 10 to reach a million BTU. If you heat with gas and want a rebate, check the form for your fuel; our rebate story explains why.

What COP should you use for an older house?

Use a range, not one figure, and be most careful at the low end. The best field evidence we have is old but useful: a Building America study from winter 2013-14 that monitored seven inverter-driven units in Connecticut, Massachusetts and Vermont. Monthly COPs ran from 1.1 to 3.1. Maximum capacities were generally in line with makers’ claims down to -10F, so the machines weren’t the main puzzle.

The wide range was the real finding. The researchers’ likely explanations were weak indoor airflow, badly sited outdoor units, high return air temperatures and thermostat setback, among others. Measured airflow came in at only 50 to 80 percent of the listed figure. All of that is about installation and use, and most of it is in somebody’s control. It’s an old study and newer equipment may do differently, but we have no comparable field study to quote, so don’t read 3.1 as a ceiling or as a promise.

Treat a monthly COP near 1.1 as a warning sign and not a typical result. It’s why reading the bid closely matters to your running costs, and it’s why placing the outdoor unit well counts for more than looks. The piece on outdoor units goes into that.

How much does a seasonal heat pump electric rate change the arithmetic?

It can lower the winter delivery part of your bill, and how much depends on your utility and your supply charge. Eversource, National Grid and Unitil offer seasonal heat pump rates to eligible customers, and the updated winter rate applies from Nov. 1, 2026 without signing up again. Find out whether you qualify before you assume anything, because a lower winter rate shows up directly in the first formula.

Eversource’s published delivery rates give a sense of the shape, for Sept. 1 to Dec. 31, 2026:

The two seasons differ by about 7.7 cents per kWh on those lines. Your all-in price is that delivery figure plus supply and any other charges, so don’t plug these numbers into the formula on their own. Use your bill. We don’t quote a National Grid figure because the one we found was out of date, and customers there should read their own tariff page. If your winter all-in figure comes to, say, $0.25 per kWh on your actual bill, use the $0.25 break-even above.

What else changes the winter bill in an older house?

Mostly the load itself, and how you share it with the old system. Sealing and insulating make every option cheaper, and ENERGY STAR puts the savings at up to 10 percent on annual energy bills. In the arithmetic, that’s a smaller number of gallons before you start, and a smaller heat pump may follow. The assessment story covers how to get that work priced.

A backup changes the sum as well. If the heat pump carries the milder months and oil the coldest stretch, you pay both bills, and the blended cost depends on when the switch happens. The Cape story on keeping the boiler deals with that choice. And the rebate form itself carries a plain warning worth repeating: unless you already heat with resistance, your electricity use goes up, often offset by fuel savings, and adding cooling where you had none raises summer use. If you take up air conditioning you didn’t have before, count it as a new comfort with a new cost rather than part of this comparison. Any comparison still counting a federal tax credit is out of date too: the IRS credit covers only property placed in service before Dec. 31, 2025.

Take your own gallons, therms and kilowatt-hours, run the two formulas at this week’s fuel price and at last year’s, and see how much COP your decision requires. If the required COP is low, the machine has plenty of margin; if it’s high, the design has to be good.