Reference tables
Look-up charts built from stable water-heating thermodynamics and labeled industry planning typicals — water-heater size (gallons + First-Hour Rating) by household, DOE hot-water use by fixture, lifespan & UEF by type, installed cost bands by type, and inlet water temperature by US region.
Typical published planning values — NOT a certified spec or professional advice. Efficiency, sizing and life vary by unit and installation; confirm on the EnergyGuide label and the manufacturer’s instructions. Water-heater installation, gas, venting, combustion, the temperature-&-pressure relief valve, and the scald / Legionella tradeoff of a temperature setting are a licensed plumber / gas fitter, manufacturer-instruction and local-code matter — not engineered here.
Water-heater size (gallons + First-Hour Rating) by householdThe signature reference: LABELED tank gallons + First-Hour Rating + tankless GPM by household — 1–2 people ≈ 30–40 gal (FHR 40–55), 3–4 ≈ 50–60 (FHR 60–75), 5+ ≈ 60–80.DOE hot-water use by fixture (gallons per use + GPM)The signature companion: LABELED DOE hot-water use per fixture — shower ≈ 20 gal, bath ≈ 20, shave ≈ 2, hand/face ≈ 4, dishwasher ≈ 6, clothes washer ≈ 7 — plus fixture flow GPM for tankless sizing.Water-heater lifespan (years) by typeLABELED typical water-heater lifespan by type — gas tank ~8–12 yr, electric tank ~10–15, tankless ~18–20, heat-pump ~10–15.Installed water-heater cost bands by typeLABELED installed $ cost bands by type (electric tank, gas tank, gas/electric tankless, heat-pump) — a sanity guide only, you enter the real price.Inlet water temperature (°F) by US regionLABELED incoming (inlet) water temperature by US region — cold/northern ~40–50 °F, temperate ~50–60, warm/southern ~60–77 — for the temperature rise ΔT.