About Physics of Buildings
Physics of Buildings explains how the systems inside homes and commercial buildings work, through their physics: pumps, tanks, water heaters, boilers, heat pumps, ducts and wires. It is written for two readers at once: the homeowner with a problem, and the technician, apprentice, student or engineer who wants the mechanism and the numbers.
This page, on water heater expansion tanks and pressure-reducing valves, is a Physics of Buildings explainer made by an AI-assisted production system: an AI agent researched the sources, wrote the text, and built the simulation and the estimator, and a separate, independent verification step checks every claim and every model against the cited sources before the page is published. There are no ads and no sign-up. It shares its pressure-tank physics with the well pressure tank page.
How the physics is checked§
Every model behind a figure is tested twice: by its author against worked examples and manufacturers’ published tables, and by an independent test suite written from the model specification and the sources alone, without reading the model’s code. Every factual claim is recorded in a claims register with its source and checked by a reviewer who did not write it. What each figure simplifies is stated next to it and collected on the sources page.
Editorial boundaries§
- We explain mechanisms and diagnosis. We do not give step-by-step instructions for work on energized electrical equipment, gas appliances, refrigerant circuits or well-pump wiring, or for installing an expansion tank or adjusting a pressure-reducing valve. Where a job involves gas, line voltage or stored pressure, we say so and say when to call a licensed professional.
- The temperature and pressure relief valve is a life-safety device. Nothing here suggests capping, plugging or disabling it.
- Codes and licensing vary by state, province and county. Nothing here is a statement of code compliance, and no estimator result is a sizing guarantee.
- Simulations illustrate mechanisms with representative numbers. They are not measurements of any particular installation.
- Manufacturers’ documents are cited because they publish the numbers installers use; citing one is not an endorsement.
Found an error?§
Please open an issue on the source repository. Corrections are welcome and credited.
Reuse§
Text and figures are licensed CC BY 4.0; code is MIT. Teachers and trainers may use and adapt any of it, with attribution.