Methodology & data sources
HeatSwap compares the annual running (energy) cost of heating a US home with a heat pump versus a natural-gas furnace, propane furnace, oil boiler/furnace and electric resistance. This page documents every source, constant, efficiency and assumption — nothing here is a black box, and nothing is fabricated.
The mild YMYL note
These are estimates for general information, not a quote or an engineering load calculation. Actual savings depend on your home's insulation, your equipment, sizing, controls, the real winter and your specific utility tariff. Verify with a licensed HVAC professional and your own bills before making a decision. See our disclaimer.
Energy-conversion constants (ENERGY STAR)
To compare fuels fairly, everything is converted to the same useful-heat unit (BTU) using the standard ENERGY STAR thermal-energy conversions (U.S. public domain):
| One unit of fuel | Energy content |
|---|---|
| 1 therm of natural gas | 100,000 BTU |
| 1 kWh of electricity | 3,412 BTU |
| 1 gallon of No. 2 heating oil | 138,500 BTU |
| 1 gallon of propane | 91,500 BTU |
Source: ENERGY STAR Thermal Energy Conversions. Data as of June 2026.
The cost formulas
- Fossil fuel: annual cost = (annual heat demand ÷ AFUE) ÷ (BTU per unit) × price per unit.
- Heat pump: annual cost = annual heat demand ÷ (3,412 × seasonal COP) × electricity $/kWh.
- Electric resistance: the heat-pump formula with COP = 1.0.
Example: a home needing 36 MMBTU/yr, heated by a 95% gas furnace at $1.80/therm, uses 36,000,000 ÷ 0.95 ÷ 100,000 ≈ 379 therms ≈ $682/yr. The same heat from a heat pump at COP 2.4 and $0.20/kWh uses 36,000,000 ÷ (3,412 × 2.4) ≈ 4,396 kWh ≈ $879/yr.
Assumed efficiencies (all editable in the calculator)
- Natural gas furnace: 95% AFUE (modern condensing).
- Propane furnace: 92% AFUE (condensing).
- Heating oil boiler/furnace: 85% AFUE (typical).
- Electric resistance: COP 1.0 (one unit in, one out).
- Heat pump: a climate-zone seasonal COP of 2.0–3.2 (see below).
Climate-zone COP presets and heat-demand bands
A heat pump's seasonal COP falls in colder climates. We use four planning zones, each with a seasonal COP (for a modern cold-climate air-source heat pump) and a per-square-foot annual heat-demand band. These are documented assumptions, not measurements of your home:
| Climate zone | Seasonal COP | HSPF2 equiv. | Heat-demand band |
|---|---|---|---|
| Hot / mild (e.g. Gulf South, Southwest) | 3.2 | ~10.9 | 8,000 BTU/sq ft/yr |
| Mixed (e.g. Mid-Atlantic, Pacific NW, lower Midwest) | 2.8 | ~9.6 | 18,000 BTU/sq ft/yr |
| Cold (e.g. Northeast, upper Midwest) | 2.4 | ~8.2 | 28,000 BTU/sq ft/yr |
| Very cold (e.g. northern New England, Mountain West, Upper Plains) | 2 | ~6.8 | 38,000 BTU/sq ft/yr |
Source: HeatSwap planning presets (consistent with DOE/AHRI cold-climate ratings). Data as of June 2026.
Reference home for state pages and rankings: 2,000 sq ft at the state's default zone. Cold-climate performance varies — on the coldest days any heat pump derates, and a backup heat source is common in severe climates.
Fuel prices (all U.S. public domain)
- Electricity: EIA Electric Power Monthly, Table 5.6.A, residential average price by state, March 2026.
- Natural gas: EIA "Price of Natural Gas Delivered to Residential Consumers" ($/Mcf), March 2026, converted to $/therm using the EIA convention 1 Mcf ≈ 10.37 therms ($/therm = $/Mcf ÷ 10.37).
- Heating oil & propane: EIA Heating Oil and Propane Update, residential price ($/gal) by PADD region (Week ending 2026-03-30, end of the 2025–26 heating season). EIA does not publish these per individual state, so each state uses its PADD-region price — disclosed on every state page.
Granularity & honesty about gaps
Electricity and natural-gas prices are per state. Heating oil and propane are per PADD region (EIA
collects them only Oct–Mar, and not per state). For 10 states EIA
published no March 2026 residential natural-gas price; those use the U.S. average
($16.25/Mcf) and are flagged ngEstimated on the page. No value is invented —
a missing figure is substituted with the clearly-labelled national average or shown as N/A.
What is out of scope
This is operating (energy) cost only. It excludes equipment price, installation, maintenance, ductwork, electrical upgrades and rebates (federal 25C tax credit, HOMES/HEAR, state and utility programs), which affect total cost of ownership. See the blog for 2026 rebate context.
Data sources
| Source | Refresh cadence | License |
|---|---|---|
| EIA Electric Power Monthly, Table 5.6.A (residential electricity price) | none | U.S. public domain |
| EIA Natural Gas — Price to Residential Consumers ($/Mcf) | none | U.S. public domain |
| EIA Heating Oil and Propane Update (residential $/gal by PADD) | none | U.S. public domain |
| ENERGY STAR Thermal Energy Conversions | none | U.S. public domain |
Snapshot compiled June 2026. Prices change — verify on the source before relying on these figures.
How calculations run
The calculator runs entirely in your browser using the formulas above; we do not store your inputs. The committed data snapshot is built by a documented script (no live network calls at build time, no GitHub Actions). See the disclaimer for limits.
Last updated: 2026-06-29