What size water heater for 1 person?
For one person, manufacturers suggest a 30–40 gallons tank. By the Department of Energy's peak-hour method, a typical 1-person home needs a First Hour Rating of about 26 gallons. Adjust your busiest hour below.
Method: U.S. Department of Energy First Hour Rating method for tanks; flow × temperature rise × 500 for tankless.
Your busiest hour of hot water use
Recommended tank
30 gallons
Peak hour demand: 26 gallons · First Hour Rating needed: 26+ gal
Cross-check: for 1 person, manufacturers such as Rheem suggest 30–40 gallons.
- • Look for a water heater with a First Hour Rating of at least 26 gallons on its yellow EnergyGuide label.
How water heater size is calculated
The U.S. Department of Energy recommends sizing a storage tank by its First Hour Rating, the gallons of hot water it can deliver in one busy hour starting full. Estimate your household's peak hour demand, then choose a heater whose First Hour Rating, printed on its EnergyGuide label, at least matches it.
| Use | Hot water per use |
|---|---|
| Showers | 20 gallons |
| Baths | 20 gallons |
| Shaving / hand washing | 2 gallons |
| Hand dishwashing / food prep | 4 gallons |
| Dishwasher loads | 7 gallons |
| Laundry loads (top-loader) | 25 gallons |
| Laundry loads (front-loader) | 15 gallons |
Tankless heaters are sized by flow instead: add up the gallons per minute of every fixture you run at the same time, and find your temperature rise from incoming water to 120°F. The heat needed in BTU per hour is flow (GPM) × rise (°F) × 500.
Water heater size by household
| People | Typical tank size |
|---|---|
| 1–2 | 30–40 gallons |
| 2–4 | 40–50 gallons |
| 5 | 50–55 gallons |
| 6+ | 65–80 gallons or tankless |
More water heater guides
Frequently asked questions
What size water heater for a family of 4?
Usually a 40–50 gallon tank. By DOE's method, a family of 4 with 3 showers in the busiest hour needs a First Hour Rating of about 68 gallons, which a 40 gallon gas or 65 gallon electric heater typically meets.
What is a First Hour Rating?
It's how many gallons of hot water a tank heater can supply in one hour, starting full. It's on the yellow EnergyGuide label and matters more than tank size.
Why do gas tanks deliver more than electric?
Gas burners reheat water faster, so a 40 gallon gas tank often has a higher First Hour Rating than a 50 gallon electric one.
What size tankless water heater do I need?
For two showers and a kitchen faucet at once, about 5.5 GPM. In a cold climate with 40°F incoming water, that means roughly 220,000 BTU/h of heat, which is near the top of residential gas units.
What temperature should a water heater be set to?
The Department of Energy recommends 120°F for most homes. It saves energy and reduces scalding risk.