Compare useful heat, not fuel input
Both systems must deliver the same heating energy. This tool uses a heating requirement in million Btu (MMBtu). One million Btu is 1,000,000 Btu. The input can describe a month or a full heating season, as long as the average COP matches that period.
Furnace therms = delivered Btu ÷ 100,000 ÷ (AFUE / 100)
Multiply each quantity by the corresponding energy price. The U.S. Energy Information Administration gives the rounded conversions used here: 3,412 Btu per kWh and 100,000 Btu per therm.
Understand the break-even COP
With $0.18/kWh electricity, $1.50/therm gas, and 95% AFUE, the break-even COP is approximately 3.34. At COP 3 and a 50 MMBtu heating requirement, the example heat pump uses 4,884.7 kWh and costs $879.25. The furnace uses 526.3 therms and costs $789.47. Every price and efficiency in that example is an editable assumption.
COP compares useful heat with electrical input in the same energy units. AFUE describes a furnace’s seasonal fuel efficiency. DOE explains these efficiency definitions. SEER2 and HSPF2 are different rating metrics and must not be typed into the COP field.
Where the comparison stops
This is variable fuel cost. It excludes installation, maintenance, fixed gas charges, furnace blower electricity, and distribution losses. Electric backup strips and defrost can change a heat pump’s effective performance. A point-temperature COP is not automatically the seasonal average. Economic break-even does not establish the outdoor temperature at which equipment can meet the home’s load; a contractor needs performance tables and a load calculation for that decision.
Calculation model reviewed October 21, 2026. Original worked examples by the Everyday Cost Lab editorial desk. Estimates do not replace a contractor’s assessment.