Water Heater Size Calculator
Estimate the first-hour rating and tank size (or tankless flow) your home needs in seconds.
A real person answers. Free estimate, no obligation.
Every number here is an estimate from public data and general rules of thumb, worked from what you entered. It can be wrong, out of date, or not fit your home, and it is not professional advice, an inspection, or an offer. Confirm anything that matters with a licensed pro or the authority named on the page, and treat any decision as your own. We are not responsible for losses that come from relying on these figures.
How water-heater sizing works
First-hour rating (FHR)
FHR is the gallons of hot water a unit can deliver in the busiest hour — the number that should match your peak demand, not just the tank size printed on the label.
Tank vs tankless
A tank stores a set number of gallons and refills between draws; a tankless unit heats on demand and is sized by flow (gallons per minute) for the fixtures running at once. We show both so you can compare capacity — never price.
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