What size water heater do I need?

Match first-hour rating to the peak hour in the house, not tank gallons to a personality type. Four people is not automatically “50 gallons.”

Where do the gallons-per-person come from?

They are editorial planning factors on this page, not a plumbing-code table. If you know fixture flow rates, those beat this tool.

Does this size a tankless unit?

No. Tankless is gallons per minute at a temperature rise. This page is FHR for storage heaters.

HyrePlumber tools

Size the first hour, not the tank sticker

A 50-gallon tank is not a 50-gallon first hour. First-hour rating (FHR) is recovery plus stored water. This tool uses editorial planning factors — 12 gallons per person, extra showers, a soaking tub, a dishwasher — labelled as such, not as a code table.

FHR on the EnergyGuide, not gallons on the carton Planning factors on this page are editorial: 12 gal/person, 8 gal/extra shower, 15 gal soaking tub, 6 gal dishwasher, then a ±15% band. Confirm against the fixture flow rates in the house.

On four people, two showers, no soaking tub, with a dishwasher, peak-hour planning volume is about 70 gallons and the FHR band is the neighbourhood to read off the yellow label. Tankless is a GPM-at-temperature-rise problem, not this tool — use tank-vs-tankless for the money, and an installer for the GPM.

People and fixtures

Planning factors, labelled as such. Nothing is emailed.

— FHR neighbourhood

— Peak-hour planning volume

— Read the label

What this assumed —

Editorial planning factors, not a code table. HyrePlumber does not size heaters as a specification.

Questions this calculator answers

What size water heater do I need?: Match first-hour rating to the peak hour in the house, not tank gallons to a personality type. Four people is not automatically “50 gallons.”
Where do the gallons-per-person come from?: They are editorial planning factors on this page, not a plumbing-code table. If you know fixture flow rates, those beat this tool.
Does this size a tankless unit?: No. Tankless is gallons per minute at a temperature rise. This page is FHR for storage heaters.

Sources and methodology

Figures dated 23 August 2026. Last reviewed August 16, 2026.

EnergyGuide — water heaters (FTC, retrieved 2026-08-23. Cited for the label that carries FHR / UEF. Not a sizing table.)

Repair vs replace Sizing is a replacement-day question.
Tank vs tankless Money, once the size conversation is honest.
Water usage calculator Daily gallons of habit are not first-hour rating. Both start with how the house actually uses water.

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People and fixtures

Questions this calculator answers

Sources and methodology

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