Every cost, saving and payback figure on Home Comfort Math comes from a public source or from a calculation we show on the page. This is how we do it.
Our sources
- U.S. Energy Information Administration (EIA): electricity, natural gas, propane and heating oil prices, national and by state, plus the Short-Term Energy Outlook and the Winter Fuels Outlook.
- ENERGY STAR and the DOE Energy Saver program: efficiency criteria, recommended settings and typical savings.
- AHRI Directory: certified efficiency ratings (SEER2, EER2, HSPF2, AFUE, UEF) for specific equipment.
- U.S. Environmental Protection Agency (EPA): refrigerant rules and related regulations.
- PVWatts, from the National Laboratory of the Rockies (formerly NREL): solar production estimates by location.
- DSIRE and official state energy office pages: state and utility rebates and incentives.
- Lawrence Berkeley National Laboratory and published marketplace reports: installed prices for solar and storage.
- U.S. Consumer Product Safety Commission (CPSC): generator and carbon monoxide safety.
- Manufacturer specification sheets and installation manuals for capacity, efficiency and operating limits.
How we calculate
We convert every fuel to the same unit so options can be compared fairly: the cost of one million BTU of heat or cooling actually delivered to your home. The conversion factors we use are standard ones:
- 1 kWh = 3,412 BTU, and 1 million BTU = 293.07 kWh
- 1 therm of natural gas = 100,000 BTU
- Propane ≈ 91,500 BTU per gallon; heating oil ≈ 138,500 BTU per gallon
- Efficiency ratings (AFUE, COP, SEER2, HSPF2, UEF) are applied as the manufacturer and the Department of Energy define them
When a figure depends on your situation, we give a range rather than a single number, explain what moves it up or down, and show a worked example with the assumptions written out. National averages are always dated, and where state data exists we use it.
Our calculators
Each calculator shows its formula and default values, and you can replace the defaults with the numbers on your own bill or quote. Calculators give estimates for planning. Sizing results are not a substitute for a Manual J load calculation by a licensed contractor, and cost results are not quotes.
How we keep numbers current
- Energy prices: reviewed every quarter, and when the EIA publishes a new outlook.
- Rebates, tax credits and regulations: reviewed every month. Every page that mentions them shows a “Last checked” date.
- Equipment and installation costs: reviewed at least once a year.
Corrections
If you find a mistake, email contact@homecomfortmath.com. We check every report, fix confirmed errors quickly and update the date on the page.
Editorial independence
Advertising and affiliate relationships never decide what we recommend. Our verdicts follow the math, and when the math says “skip it,” we say so. Articles are published by the Home Comfort Math Editorial Team; learn more on our About page.