Credits, data sources and licences

Our own content

The calculators, their explanations, the worked examples and the Knowledge Center articles are written for this site. Each calculator page lists the sources of its formulas and constants under “References”. Formulas, physical constants and short factual values are cited to their sources; we do not reproduce tables or text from copyrighted standards, handbooks or manufacturer literature.

Copyrighted standards

ACCA manuals (J, D, S), ASHRAE handbooks and standards, NFPA codes including the National Electrical Code, ICC codes, AMCA and SMACNA publications are copyrighted. We name them where they are the professional reference and link to official pages, but we do not copy their tables. Where a calculation would depend on a table we cannot reproduce — for example code minimums, equivalent lengths of fittings or conductor sizing — the calculator asks you to enter the value, or we do not offer that calculation.

Public data we use

• ENERGY STAR certified product data, the room air conditioner sizing chart and program guidance — U.S. Environmental Protection Agency (U.S. Government works).
• Energy prices and energy contents — U.S. Energy Information Administration.
• Design temperatures for the climate-zone presets and the design-temperature pages — NOAA National Centers for Environmental Information / U.S. Air Force, Engineering Weather Data (U.S. Government work).
• Refrigerant leak-rate rules — U.S. EPA, Code of Federal Regulations; pipe roughness and friction-factor method — U.S. EPA, EPANET 2.2 User Manual.
• Water properties used to check our tables — NIST Chemistry WebBook. Refrigerant charge verification tolerances — California Energy Commission.
• Guidance and worked examples from the U.S. Department of Energy, NIST, IRS, OSHA, CFPB and other federal agencies (U.S. Government works).
• Other sources are cited where they are used, such as state agency guidance, NREL and national laboratory reports, and university or trade publications; we cite them and do not copy their tables.

Open-source software, fonts and data tools

The site runs on open-source software under permissive licences (MIT, ISC, Apache-2.0, 0BSD and others), and uses the Bricolage Grotesque typeface under the SIL Open Font License 1.1. Psychrometric calculations follow the ASHRAE equations and are checked against PsychroLib (MIT). Refrigerant property tables are generated with CoolProp (MIT). The full list of packages, versions and licence texts is in the third-party notices, generated with every release.

Trademarks

ENERGY STAR and the ENERGY STAR mark are registered trademarks owned by the U.S. Environmental Protection Agency. ACCA, ASHRAE, NFPA, National Electrical Code and other names are trademarks of their owners. Equipment brand and model names shown in our heat pump comparison come from the ENERGY STAR dataset and belong to their manufacturers. This site is independent: it is not affiliated with, sponsored by or endorsed by any of these organisations or manufacturers.

Concerns

If you believe something on this site uses your work without permission or credits it incorrectly, please tell us through the contact form. We review every report promptly and correct or remove material where needed, as described in our corrections policy.