Methodology
Every number on the site comes from one of the data sources below, run through one of the formulas below.
Data sources
Electricity comes from EIA's monthly residential revenue, sales and customer accounts by state (Electric Power Monthly), currently through July 2026. Average price is revenue divided by kWh sold, average bill is revenue divided by customer accounts, and average use is kWh sold divided by accounts.
Natural gas comes from EIA's monthly price of gas delivered to residential consumers and the heat content of the gas delivered, by state (Natural Gas Monthly), currently through July 2026.
Heating oil and propane come from EIA's weekly residential prices in the State Heating Oil and Propane Program, collected from October through March. The latest week is October 5, 2026.
The site downloads EIA's published bulk data, which needs no account or key, checks it weekly, and rebuilds pages when a figure changes.
Seasons
Heating calculations use prices from the last complete heating season, November through March, because winter prices differ from annual averages: summer electricity rates are higher in many states, and summer gas prices per unit are inflated by fixed charges spread over little use. Electricity's seasonal price is revenue divided by kWh over those five months.
Formulas
- Energy used: kWh = watts × hours ÷ 1,000.
- Running cost: kWh × price per kWh.
- Gas price per therm: price per thousand cubic feet ÷ (heat content in Btu per cubic foot × 1,000 ÷ 100,000).
- Cost of heat: price per unit of fuel ÷ heat content per unit ÷ efficiency, in dollars per million Btu delivered.
- Heat pump seasonal efficiency: HSPF2 ÷ 3.412 Btu per watt-hour, giving units of heat per unit of electricity.
- Heat a home needed: fuel burned × heat content × the old system's efficiency.
Constants
3,412 Btu per kWh, 100,000 Btu per therm, 91,452 Btu per gallon of propane and 138,500 Btu per gallon of heating oil, from EIA's Btu conversion factors. Natural gas uses each state's measured heat content instead.
Federal minimum efficiencies come from 10 CFR 430.32: 7.5 HSPF2 for split-system heat pumps made since January 1, 2023, and 80% AFUE for non-weatherized gas furnaces until December 18, 2028, rising to 95% after that date.
Assumptions you can change
Where a calculator needs equipment you have not described, it assumes a new installation: a 95% furnace for gas and propane, an 85% oil furnace, and a heat pump rated 8.5 HSPF2. These are choices, not facts, and every calculator lets you replace them.
What the estimates leave out
State averages hide differences between utilities, rate plans and fixed charges. Heat pump ratings are measured for a moderate climate and overstate efficiency in very cold places. Installation costs, maintenance and taxes on equipment are not included anywhere.
Last updated October 17, 2026