As a general guide, a 1–2 person home needs a 30–40 gallon tank water heater, a 3–4 person home needs 40–50 gallons, and a 5+ person home needs 50–80 gallons. For tankless units, size by flow rate: most homes need 6–10 gallons per minute (GPM). Getting the size right matters – too small and you run out of hot water, too large and you pay to heat water you never use. Here's how to choose.
Tank Water Heater Sizing by Household
- 1–2 people: 30–40 gallons
- 2–3 people: 40–50 gallons
- 3–4 people: 50–60 gallons
- 5+ people: 60–80 gallons
These are starting points – usage habits matter as much as headcount.
The Better Way to Size a Tank: First-Hour Rating
The most accurate way to size a tank isn't just gallons – it's the First-Hour Rating (FHR), which measures how much hot water the unit can deliver in a busy hour. Estimate your peak hour (say, back-to-back morning showers plus the dishwasher) and match the FHR to it. A good rule: figure about 12 gallons of hot water per person during your busiest hour.
Sizing a Tankless Water Heater (GPM)
Tankless units are sized by flow rate in gallons per minute (GPM) – how many fixtures can run hot water at once. Add up the GPM of the fixtures you'd realistically use simultaneously:
- Shower: ~2–2.5 GPM
- Kitchen faucet: ~1.5 GPM
- Bathroom faucet: ~1 GPM
- Dishwasher / washing machine: ~1.5–2 GPM
Most San Tan Valley homes land in the 6–10 GPM range. Our hot incoming water temperature actually works in your favor here, letting a tankless unit deliver more usable flow than in colder climates.
What Else Affects the Size You Need
- Number of bathrooms and simultaneous use.
- Peak-hour habits – everyone showering in one window needs more capacity.
- Appliances that draw hot water (dishwasher, washer).
- Fuel type – gas units generally recover (reheat) faster than electric.
What Happens If You Size It Wrong?
Too small, and you'll run out of hot water during busy times and wear the unit out faster from constant demand. Too large, and you pay more upfront and waste energy keeping extra water hot. The right size balances comfort and efficiency – which is why a quick professional assessment is worth it before you buy.
Get the Right-Sized Water Heater in San Tan Valley
Not sure which size fits your home and habits? Az Express Plumbing will assess your household and recommend the right tank or tankless unit – then install it correctly. See our water heater services, compare options in our tank vs. tankless guide, or call (480) 771-7519 today.
