How Our Calculators Work
Every estimate on this site uses a straightforward formula. Here's exactly how we calculate heating costs — no black boxes, no guesswork.
The Core Formula
Electric heater: Cost = (Watts ÷ 1,000) × Hours × Rate ($/kWh)
Any fuel, per delivered heat: $/MMBtu = (Price ÷ BTU per unit) ÷ Efficiency × 1,000,000
Whole house, per month: BTU = UA × (65°F − outdoor avg) × 30 days × 24 hours
We start with the heat your home or heater actually delivers
Electric heaters are rated in watts; 3,412.14 BTU is one kWh, so a 1,500 W heater produces about 5,100 BTU/hr — a useful reality check against "heats 1,000 sq ft" marketing. For a whole house we model heat loss instead: a heat loss coefficient in BTU per hour per °F, multiplied by the temperature difference the heating system has to bridge.
We convert that into fuel, using real efficiency
A furnace does not turn every BTU of fuel into delivered heat, and a heat pump delivers more heat than the electricity it consumes. So we divide by AFUE for combustion equipment (92% for a modern condensing gas furnace, 80% for propane, 85% for oil) and by the coefficient of performance for a heat pump. Electric resistance heaters — ceramic, convection, infrared, oil-filled, baseboard — are all treated as 100% efficient, because they all are.
We apply a price, and name the series it came from
Defaults are 18.44¢/kWh, $1.44/therm, $2.55/gal propane and $3.98/gal heating oil, each carrying its own EIA series and reporting period rather than a bare year. Every calculator lets you replace the default with the rate on your own bill, which is always the better number.
We express the answer per 1,000 BTU delivered
Dollars per gallon, per therm and per kWh cannot be compared to each other. Dollars per 1,000 BTU of heat actually delivered into the room can be. That is the unit our comparison tables use, and it is why the ranking sometimes disagrees with the usual folklore about which fuel is cheapest.
Monthly and seasonal figures use heating degree days
A winter month's heat demand is the home's heat loss coefficient multiplied by heating degree days — the gap between a 65°F base temperature and the local December–February average, times the hours in the month. Seasonal totals assume a five-month heating season. Where a state's average winter temperature is above 65°F, the model returns no heating load at all, which is the honest answer.
Heater sizing uses about 10 watts per square foot
An average-insulated room needs roughly 10 watts of electric resistance heat per square foot — about 34 BTU/hr per square foot. A 1,500 W heater therefore suits a room of about 150 sq ft. Manufacturer coverage claims are routinely five to ten times that; where we quote one, we label it as the manufacturer's figure and print the 10 W/sq ft number beside it.
Data Sources and Reporting Periods
- EIA Electric Power Monthly, Table 5.6.A — May 2026, released July 23, 2026. A single month, not an annual average.
- EIA Natural Gas Monthly, residential price by state — winter average, November 2025 - March 2026 (US); December 2025 - February 2026 (by state). Winter figures, because the residential series distorts badly in summer.
- EIA State Heating Oil and Propane Program (weekly) — heating-season average, October 2025 - March 2026. Weekly October to March only; nothing published since 30 March 2026.
- EIA Winter Fuels Outlook — winter 2025-26 forecast, published October 15, 2025. Forecast expenditure, not measured outturn.
- NOAA station normals via Current Results — December-February averages, for heating degree days.
- DOE fuel heat contents and manufacturer efficiency ratings (AFUE, HSPF, COP).
Last refreshed August 22, 2026. Electricity updates monthly with the Electric Power Monthly; gas monthly with the Natural Gas Monthly; propane and heating oil weekly through the heating season only.
What the Model Deliberately Does Not Do
- It does not include fixed monthly customer charges, tiered blocks, demand charges or time-of-use pricing — only the energy rate.
- It does not know your building. Air tightness and insulation can move a real bill by more than a change of fuel would.
- It does not apply efficiency differences between types of electric resistance heater, because there are none: thermal mass and radiant fraction change comfort and run time, not energy consumed per hour at a given wattage.
- It does not include federal tax credits. IRC §25C and §25D both terminated for property placed in service after 31 December 2025, so payback figures on this site assume you pay the full installed price.