Recommended
50 gal
tank size
48 gal
peak-hour demand
4
people
Gas tanks recover faster, so a smaller gas tank can match a larger electric one.
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How this is calculated
Tank: sized by household occupants against typical peak-hour demand (about 12 gallons per person). Tankless: required flow = simultaneous hot fixtures × 2.5 GPM, at a temperature rise of 120°F minus your incoming water temperature.
These are standard rules of thumb for planning. Fuel type, recovery rate, and the actual fixture mix affect the final pick — confirm the model spec before installing.
This is a planning estimate — always confirm against code, spec, and your supplier before ordering or installing.
Water Heater Size Calculator: FAQ
What size water heater do I need?
For a storage tank, size by household: about 30 gallons for 1 person, 40 for 2, 50 for 3–4, and 65–80 for 5 or more. Gas tanks recover faster than electric, so a smaller gas tank can serve the same household. For tankless, size by flow rate instead.
How do I size a tankless water heater?
Add up the flow of the hot-water fixtures you’d run at once (about 2.5 GPM each), then check the incoming water temperature — the colder it is, the bigger the temperature rise to 120°F and the lower a unit’s usable flow. Pick a unit rated for your GPM at that rise.
Tank or tankless?
Tankless heats on demand, never runs out, and saves space and standby energy, but costs more up front and has a flow-rate ceiling. Tank is cheaper to install and delivers a big burst easily, but can run out and loses standby heat. Household size and simultaneous demand drive the choice.
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