Methodology
How the home energy calculators on BuildCalc work, and what their numbers do and do not mean.
Formulas
Electricity: kWh = watts ÷ 1,000 × hours. Cost = kWh × electricity rate.
Heat pump: electricity needed = heating demand ÷ COP. Furnace and gas water heater: fuel therms = (demand ÷ efficiency) ÷ 29.307, because 1 therm = 29.307 kWh.
EV: monthly kWh = miles × kWh per 100 miles ÷ 100. Solar payback: annual generation = system size × production per kW, payback years = system cost ÷ (generation × rate).
Data sources
Default values are typical US figures used as editable starting points. They are not a claim that a rate is current for your state or utility. For real rates, use your electricity or gas bill, your utility website, or the US Energy Information Administration (EIA) for state averages. For vehicle fuel economy, use fueleconomy.gov. For a real solar or heat pump quote, use a local installer.
What is not included
Running-cost calculators do not include purchase price, installation, maintenance, taxes, delivery charges or fixed fees, unless a calculator has a separate fixed-fee field. Payback and saving results are estimates, not guarantees.