How the heating cost comparison works.

A gallon of oil, a therm of gas, and a kilowatt-hour each contain a different amount of raw energy, and each heating system converts that energy into usable heat at a different efficiency. To compare them fairly, every fuel is converted to the cost of one million BTU (MMBtu) of heat actually delivered to the home:

For a heat pump, efficiency is the seasonal COP (coefficient of performance: heat delivered per unit of electricity, averaged over the heating season), so the electricity term becomes (¢/kWh ÷ 100) × (1,000,000 ÷ 3,412) ÷ COP. Annual figures multiply the per-MMBtu cost by the annual delivered heating demand you enter — delivered heat the home used, not the gross fuel energy you bought. Nothing is compounded, discounted, or projected; this is a comparison of the prices entered on the page, not a forecast.

National calculator. Heating oil $5.535/gal and propane $2.674/gal are the final weekly EIA readings of the 2025–26 season (March 30, 2026; that survey resumes in October). Natural gas $1.46/therm is the midpoint of the derived-from-EIA 2025–26 heating-season band ($1.35–$1.57). Electricity defaults to the EIA national residential average for April 2026 (18.83¢/kWh, a historical reading; the live table now shows a later month) with Census-division overrides from the same release (for example New England 29.49¢). Sources: EIA weekly heating oil and propane prices, EIA natural gas residential price, EIA Electric Power Monthly Table 5.6.A.

Portland, Maine calculator. Heating oil ($5.33/gal) and propane ($3.59/gal) are the Maine Department of Energy Resources survey readings for Southeast / Greater Portland, September 8, 2026. They are spot cash survey averages, not quotes; the propane survey basis is a 30-day cash/credit price at 900 or more gallons a year. Electricity defaults to 24.68¢/kWh: the actual CMP Rate A residential tariff (2026 standard-offer supply 12.721¢ plus volumetric delivery 11.959¢, above the first 50 kWh/month) from the Maine PUC residential rate table as of July 1, 2026 and CMP's pricing page, both checked September 9, 2026. The $27.37 monthly service charge is excluded from the per-kWh figure because it does not change with incremental heating use for a customer keeping electric service. The EIA Maine state average (29.59¢, June 2026, released August 26, 2026) is offered in the utility selector as a dated fallback. Natural gas remains a national average because no Portland-area gas tariff was sourced; it is labeled "not a Maine rate" on the page.

Utility rate versus state average. Where an actual utility tariff exists it is used and labeled with its effective date; state or regional averages are labeled as dated fallbacks. Note the difference in what they contain: the CMP tariff default excludes the fixed monthly charge, while EIA average-revenue figures spread fixed charges over kWh, and the tool does not model adding or removing a utility account. Your own bill always beats both.

Planned re-review: EIA electricity and natural gas figures roughly quarterly; heating oil and propane weekly with the DOER survey through the heating season; the CMP tariff monthly and before its next effective change; Maine program terms around known transitions, including the insulation program's September 30, 2026 completion date. This is the planned cadence, not a log of past checks; each page shows the date its defaults were actually last checked. To report a wrong figure, email [email protected] with the page and the number.

Pages using this methodology: national heating fuel comparison and Portland, Maine heating cost calculator.