Water Heater Size Calculator
Determines proper water heater capacity based on household size and peak demand
Number of people in the household
Total number of bathrooms in the home
How heavily hot water is used in the household
Select all options to see recommendations
Gallons per minute for a tankless system
Amount of hot water available in the first hour
Frequently Asked Questions
What size water heater do I need?
For 1-2 people, a 30-40 gallon tank is typically sufficient. For 3-4 people, choose 40-50 gallons. Households of 5 or more should look at 50-80 gallon tanks. The right size also depends on usage patterns and how many fixtures run simultaneously.
What is first hour rating?
First hour rating (FHR) measures how many gallons of hot water a tank can deliver in its first hour of use starting fully heated. It accounts for both stored hot water and recovery rate. Match your FHR to your peak hour demand for the best performance.
Should I get a tank or tankless water heater?
Tank heaters cost less upfront and work well for steady demand. Tankless heaters cost more to install but save energy by heating water only on demand. Tankless is better for small households or homes with natural gas; tanks are simpler for high simultaneous demand.
How do I calculate peak hot water demand?
Add up the flow rates of all fixtures you might use at the same time. A shower uses about 2 GPM, a dishwasher about 1.5 GPM, and a washing machine about 2 GPM. If you run a shower and dishwasher together, your peak demand is about 3.5 GPM.
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