INSIDE THE PUBLICATION
Sources & Methodology
Our approach combines primary-source evidence with transparent calculations. A useful number needs a unit, a time period, an assumption, and a clear explanation of what it excludes.
Four kinds of information
| Type | How it is presented |
|---|---|
| Verified factual claim | A nearby source link and source notes explain the evidence. |
| Published price estimate | The original publisher, scope, and limitations are identified. |
| Calculated example | The formula, units, inputs, and exclusions are shown. |
| Editorial analysis | A decision framework or interpretation, not a measured market fact. |
Electricity and heating calculations
Electricity consumption in kWh equals electrical input in kW multiplied by operating hours. Cost equals kWh multiplied by the marginal electricity price in dollars per kWh. Our calculator uses the rounded conversion of 3,412 BTU per kWh and 100,000 BTU per therm. Heat-pump electrical input equals delivered heat divided by COP; furnace fuel input equals delivered heat divided by AFUE as a decimal.
COP is not a constant for every outdoor temperature. SEER2 and HSPF2 are seasonal ratings under specified test conditions, not direct promises of a household bill. Our comparisons exclude fixed utility charges unless the accompanying example says otherwise.
Our homepage comparison, reproduced
At $0.18/kWh, COP 3, $1.50/therm, and 90% AFUE: 1,000,000 ÷ 3,412 ÷ 3 × $0.18 = $17.58 for the heat pump. For gas, 1,000,000 ÷ 100,000 ÷ 0.90 × $1.50 = $16.67. Resistance heat uses COP 1, giving $52.75. These illustrative inputs are not national averages.
What online estimates cannot tell you
Actual runtime, delivered capacity, installation quality, duct losses, weather, fuel bills, and building loads can change the outcome. A room-by-room load calculation and properly scoped contractor quotes are more useful than a square-footage rule for selecting equipment.
Research priorities
We use current IRS guidance for federal credits, official state and utility pages for rebates, EIA for fuel-unit context, ENERGY STAR and DOE research resources for equipment guidance, ACCA for load-calculation context, and manufacturer documents for specific equipment behavior. Sources are recorded on each article with the claims they support.
Try the calculators to inspect the assumptions directly.