Water-heater size (gallons + First-Hour Rating) by household

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.

This is our own sizing matrix and the moat behind the site. For every household size it gives the LABELED storage gallons, First-Hour Rating and tankless GPM, so you can turn a household into a starting size — then beat it with the peak-hour-demand method (required FHR = Σ uses × gallons-per-use). It is a dated snapshot of published DOE / manufacturer planning ranges, not a live feed. See how it’s derived in the methodology, and use it with the what-size-water-heater calculator, the peak-hour-demand calculator and the size-by-household reference.

Recommended storage tank size (gallons) by household1–2 people30–40 gal2–3 people40–50 gal3–4 people50–60 gal5+ people60–80 gallarger household → bigger tank + higher First-Hour Rating →
HouseholdStorage tank (gallons)First-Hour Rating (gal)Tankless (GPM)
1–2 people30–4040–553–5
2–3 people40–5050–655–7
3–4 people50–6060–756–8
5+ people60–8075–908–10

LABELED published planning snapshots — confirm your unit’s rated First-Hour Rating and GPM on its EnergyGuide label. The household band is a starting point; always beat it with the peak-hour-demand method for your actual routine, and round up. Snapshot: 2026-07-13.

Related calculators

What Size Water Heater Do I NeedSize a water heater by the DOE first-hour-rating method — add your busiest hour of hot-water use to get the tank gallons and First-Hour Rating you need.Peak-Hour Hot-Water DemandAdd up every hot-water draw in your busiest hour — showers, baths, shaves, dishwashers — to find the peak-hour demand that sets the First-Hour Rating you need.Size by HouseholdGet the recommended storage tank gallons, First-Hour Rating and tankless GPM band for your household size, then confirm it with the peak-hour demand method.