Heating Cost Calculator: Gas, Propane, Oil, Electric and Heat Pump

The formula: cost per delivered BTU

Fuels are sold in different units (therms, gallons, kilowatt-hours) and burned or converted at different efficiencies. Converting every option to the price of one million BTU of heat actually delivered into the house puts them on the same footing.

Delivered BTU per unit = Energy content × Efficiency
$ per MMBtu delivered = Price ÷ Delivered BTU per unit × 1,000,000
Seasonal cost = Seasonal heat (MMBtu) × $ per MMBtu
Estimated seasonal heat (BTU) = Floor area × Heat-loss coefficient × HDD65 × 24

Energy content used here: natural gas 100,000 BTU per therm, propane about 91,500 BTU per gallon, No. 2 heating oil about 138,500 BTU per gallon, electricity 3,412 BTU per kWh. For gas billed in hundred cubic feet (CCF), one CCF is roughly 1.02–1.04 therms; most bills state the conversion.

Worked example

Natural gas at $1.50 per therm in a 95% AFUE furnace, for a house needing 50 million BTU of delivered heat a season:

1. Delivered per therm = 100,000 × 0.95 = 95,000 BTU
2. Cost per MMBtu = 1.50 ÷ 95,000 × 1,000,000 = $15.79
3. Therms used = 50,000,000 ÷ 95,000 ≈ 526
4. Seasonal cost = 526 × $1.50 ≈ $789

Swap to a heat pump at $0.16 per kWh with a seasonal COP of 3: delivered per kWh = 3,412 × 3 = 10,236 BTU, so $15.63 per MMBtu and about $782 for the season, almost identical. Electric resistance heat at the same rate costs $46.89 per MMBtu, three times as much.

Without a heat figure: set the seasonal heat source to the home-size estimate. With the defaults (2,000 sq ft, average construction at 0.25 BTU/h·°F per sq ft, 5,000 heating degree days):

1. Estimated heat = 2,000 × 0.25 × 5,000 × 24 = 60,000,000 BTU = 60.0 million BTU
2. Therms used = 60,000,000 ÷ 95,000 ≈ 632
3. Seasonal cost ≈ 632 × $1.50 ≈ $947

With the source left on "use my number", the calculator still shows the 60.0 million BTU estimate as a cross-check against your own figure.

Comparison at example prices

Example prices only; plug in your own because utility rates vary widely by state and season.

A full fuel-by-fuel discussion, including break-even electricity prices, is in gas vs electric heating.

Estimating your seasonal heat need

From last winter's bills (best): take the fuel used for heating only, multiply by energy content and by the old system's efficiency. For example, 700 therms of heating gas in an 80% furnace = 700 × 100,000 × 0.80 = 56 million BTU delivered. Subtract summer-month usage first so water heating and cooking are not counted.

From heat loss and degree days: take the house's loss per °F (the UA value from the heating BTU calculator), multiply by 24 hours and by your location's annual heating degree days (base 65 °F), then divide by 1,000,000. The raw result usually overstates real use, because sun and internal gains cover part of the load, so multiplying by roughly 0.6–0.8 is a common adjustment. A house with a UA of 700 BTU/h·°F in a 5,000 degree-day climate: 700 × 24 × 5,000 = 84 MMBtu, or about 50–67 MMBtu after adjustment.

From home size (quickest): the calculator's home-size option uses a per-square-foot heat-loss coefficient in place of a measured UA value: about 0.18 BTU/h·°F per sq ft for a tight, well-insulated house, 0.25 for average construction and 0.35 for a leaky or poorly insulated one. Seasonal heat = floor area × coefficient × HDD65 × 24. These are rough typical values, so treat the answer as a first estimate and prefer bill data when you have it. Heating degree days for your nearest weather station are published by NOAA and many utilities; approximate annual HDD65 figures are about 200 in Miami, 2,800 in Atlanta, 4,200 in Washington DC, 5,900 in Denver, 6,300 in Chicago and 7,600 in Minneapolis.

Choosing the efficiency figure

• Furnaces and boilers: use the AFUE from the nameplate or AHRI listing. Older systems with leaky ducts in unheated space deliver less than their AFUE suggests.
• Electric resistance (baseboard, electric furnace, space heaters): COP is 1.0 by definition. The electric heater running cost page covers portable heaters.
• Heat pumps: use a seasonal COP, not the 47 °F rating. A rough seasonal COP is HSPF2 ÷ 3.412 for the climate the rating represents; colder regions land lower. The COP calculator and heat pump running cost page go deeper.

Fixed charges such as a monthly gas connection fee or a propane tank rental are not included in the per-BTU figure. If switching fuels would let you drop a service entirely, add those savings separately.

Reducing the seasonal number

The seasonal cost is the product of two things: how much heat the house needs and how much each unit of heat costs. The calculator helps with the second. For the first, the biggest levers are air sealing, attic insulation and thermostat settings. Lowering the thermostat by several degrees for eight hours a day typically trims heating energy by a few percent to around 10%, more in milder climates. On heat pump systems, a thermostat that avoids firing the heat strips during morning recovery can matter even more. Insulation targets for your climate zone are in the insulation R-value chart.

What the calculator does not include

The estimate covers fuel only. It leaves out electricity for furnace blowers and boiler pumps (often $50–150 a season), maintenance, equipment cost and price swings over the winter. Heating oil and propane prices in particular can move sharply from year to year. Run the calculator at a low and a high price to see the range you are exposed to.

Frequently asked questions