Water Heater Size Calculator
Create a preliminary storage water-heater estimate from peak shower demand, other hot-water use, recovery rate, reserve and temperature rise.
Default project preview
40 gallons
Shower demand
40 gal
Recovery credit
20 gal/hr
First-hour guide
60 gal
Storage requirement
35 gal
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Peak demand = shower count × duration × flow + other demand, with reserve. Storage need = peak demand − one-hour recovery, rounded up to a planning tank size.
FAQ
Water Heater Size Calculator questions
What is first-hour rating?+
It describes how much hot water a storage heater can deliver during a high-demand first hour, combining stored water and recovery.
Why does incoming-water temperature matter?+
Colder incoming water requires more energy and can reduce recovery performance.
Can this size a tankless heater?+
Not directly. Tankless systems are selected by simultaneous flow and required temperature rise rather than storage volume.