Sources
Every organization this site relies on, and when it last changed
The methodology page lists every individual figure, its formula role, and its own retrieval date. This page answers two shorter questions instead: which organizations does this site actually depend on, and what changed here, and when.
Data and regulatory sources
| Publisher | What this site uses from them |
|---|---|
| U.S. Energy Information Administration | Residential electricity and natural gas prices by state, propane prices, and standard energy conversion factors. |
| NASA Langley Research Center, POWER Project | Twenty-year monthly climate record — air temperature, humidity, wind, surface irradiance — for every location this site models. |
| NOAA National Centers for Environmental Information | Independent thirty-year station-normal cross-check on air temperature. |
| U.S. Department of Energy | Consumer pool heater efficiency rulemaking (88 FR 34624): compliance dates, equipment lifetime, and the reasoning behind the current federal standard. |
| U.S. Government Publishing Office / National Archives (eCFR) | The codified federal minimum thermal efficiency for gas-fired pool heaters, 10 CFR 430.32(k). |
10 CFR 430.32(k)(1) — "Gas-fired pool heaters manufactured on and after April 16, 2013 and before May 30, 2028, shall have a thermal efficiency not less than 82%."
U.S. Government Publishing Office / National Archives — eCFR, Title 10, Part 430 · retrieved 2026-08-06
This is the one figure on this list worth reading in full: a federal regulation, quoted rather than paraphrased, with the exact section number attached. It is the default gas-heater efficiency used throughout this site precisely because it is the one figure knowable without a specific model number — every real unit sold today meets or exceeds it, so it is a safe floor rather than an optimistic guess.
The physics itself
The numbers above feed a model, and the model is built from published correlations with their own named authors, not invented for this site:
| Source | What it provides |
|---|---|
| ASHRAE Handbook — HVAC Applications | The Carrier evaporation correlation this site's heat-loss model is built on. |
| AHRI Standard 1160 | The rating condition every published pool heat-pump capacity and COP figure is measured at. |
| Bowen (1926), Physical Review | The sensible-heat ratio behind the convection term. |
| Swinbank (1963), Quarterly Journal of the Royal Meteorological Society | The clear-sky radiant-temperature correlation behind the night-sky radiation term. |
| Buck (1981, rev. 1996), Journal of Applied Meteorology | The saturation vapour-pressure equation every evaporation and convection figure depends on. |
None of these five is linked, because none of them publishes a free copy online — the ASHRAE Handbook is a paid standard, and the four journal articles sit behind their publishers' paywalls. They are cited by name and year so the claim is checkable in a library or through the publisher, the same treatment the methodology page gives them.
What this site does not currently have a properly checked figure for
Installed equipment cost, installer labor rates, and permit fees are all genuinely useful things to publish sourced figures for, and this site does not currently have any it is confident enough in to show a reader. A first attempt was pulled after review found it could not stand behind those specific numbers; NEEDS-CAPTURE.md in this site's repository lists exactly what is needed and from where, for a future update with a verified source. Until then, the price drivers, reading a quote and permits and code pages discuss those topics in general terms rather than citing a number this site cannot stand behind.
The bar for adding one back is the same bar every other figure on this site already clears: fetch the actual page, save the raw response, and check the specific number against those saved bytes before it goes anywhere near a reader. A number that merely sounds plausible, or that several unrelated web pages happen to agree on, does not meet that bar on its own — agreement between pages can mean independent confirmation, or it can mean the same wrong number copied around, and there is no way to tell the two apart without the underlying document in hand.
Update log
Dated entries, most recent first. An entry here does not replace the per-figure retrieval dates on the methodology page; it exists so a reader can see what changed about the site itself — new pages, corrected figures, removed claims — without comparing every page against its last visit.
| Date | What changed |
|---|---|
| 2026-09-24 | Added price-drivers, reading-a-quote, permits-and-code, when-not-to-heat, worked-examples and this sources page. An earlier draft of this batch also added an installed-cost page and figures for installed cost, labor wages, contractor-estimate guidance and one permit fee schedule; those were removed after review because they could not be properly checked against their cited sources and are listed in NEEDS-CAPTURE.md instead of being published unverified. No existing calculator, formula, or previously published figure was changed. |
| 2026-08-24 | Verbatim excerpt registry added and machine-checked against captured document bytes; federal rulemaking and definitional excerpts brought onto the climate, energy-prices, electric-resistance, swim-season and payback pages. |
| 2026-08-06 | Site rebuilt on the measured-quantities engine: twelve calculators deriving heat loss, sizing, equipment performance and season cost from a homeowner's own measurements, climate record and published energy prices. Initial figure and data retrieval date for the climate, energy-price and federal-standard registry. |
How a correction gets here
The contact page is the route to report a figure that looks stale or wrong. A correction lands in the figure registry first — the single file every page reads from — and then as a dated line in the log above, so the history of what this site has claimed stays visible rather than being silently edited away. Reporting that a specific number does not match its cited source is the single most useful kind of message this site can receive, because it is the one class of error a build check cannot catch on its own — a check can confirm a figure has a publisher, a URL and a date attached to it, but not that the number is still what that page actually says.