WaterHeaterSize Tip

What size water heater for a family of 4?

A family of four typically needs a tank with a first-hour rating of about 50 gallons, often a 50-gallon electric or a 40-gallon gas heater. WaterHeaterSize starts with a typical busy morning: three showers, one shave, some dishes, a dishwasher load and a washer load add up to 49 gallons. Change the numbers to match your household; if two teenagers shower back to back, add them.

Uses of hot water in the busiest hour of the day:

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    For tankless, two showers and a faucet at once is a common family-of-four design point: about 5 GPM.

    How the water heater size calculator works

    Tank heaters are sized by their first-hour rating (FHR): how many gallons of hot water they deliver in one busy hour, starting with a full tank. WaterHeaterSize adds up your peak-hour demand with the US Department of Energy worksheet figures per use: shower 10 gal, bath 20, shaving 2, hand dishwashing or food prep 4, dishwasher 6 and clothes washer 7. Pick a heater whose FHR is at least that total. Tankless heaters are sized by flow and temperature rise instead: the flow of every fixture that may run at once (shower 2.0 GPM, bathroom faucet 1.0, kitchen faucet 1.5, tub 4.0, dishwasher 1.0, washer 2.0) times the rise from the incoming water to the setting. Heat needed = GPM × 500 × rise in °F, in BTU per hour; divide by efficiency for gas input, or by 3,412 for electric kW.

    Tankless size by flow at a 70°F rise (50°F water heated to 120°F)

    FlowHeat outputGas input at 95%ElectricAmps at 240 V
    1 GPM35,000 BTU/h36,842 BTU/h10.3 kW43 A
    2 GPM70,000 BTU/h73,684 BTU/h20.5 kW85 A
    3 GPM105,000 BTU/h110,526 BTU/h30.8 kW128 A
    4 GPM140,000 BTU/h147,368 BTU/h41 kW171 A
    5 GPM175,000 BTU/h184,211 BTU/h51.3 kW214 A
    6 GPM210,000 BTU/h221,053 BTU/h61.5 kW256 A

    Groundwater is colder in northern climates in winter (often 40°F or less), which raises the rise and the size you need. Low-flow fixtures reduce it. Gas units need correctly sized gas lines and venting, and electric units need a dedicated circuit; have a licensed installer confirm the final choice. Results are estimates for planning.

    Frequently asked questions

    Is a 40-gallon water heater enough for a family of 4?

    Often, if it is gas with a first-hour rating of about 65–75 gallons. A 40-gallon electric tank usually has a lower FHR and may run short.

    What size tank for a family of 5?

    Add a shower (10 gal) to the family-of-four total, about 59 gallons of first-hour rating. Compare FHRs on the labels rather than tank sizes.

    What size tankless for a family of 4?

    About 5 GPM at your winter temperature rise, which is usually a 180,000–199,000 BTU gas unit.

    Is WaterHeaterSize free?

    Yes, with no sign-up or ads.

    Are my numbers saved?

    Yes, in this browser only.

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