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Your HouseholdAffiliate Disclosure: This calculator is free to use. Some product links are affiliate links. Product links and pricing are for the US market.
How This Calculator Works
- Tank sizing: Based on First Hour Rating (FHR), which measures how many gallons of hot water the tank delivers in the first hour of use. FHR must meet or exceed your peak hour demand.
- Tankless sizing: Based on flow rate (GPM) and temperature rise needed. A shower uses 2-2.5 GPM. Kitchen faucet uses 1.5 GPM. The unit must heat water from incoming ground temperature to 120F at your combined flow rate.
- Climate matters for tankless: Colder incoming water requires more heating power. A tankless rated for 5 GPM in Arizona may only deliver 3.5 GPM in Minnesota at the same output temperature.