Tankless Water Heater Sizing Calculator

Calculate the exact GPM and BTU requirements for your home based on your climate zone, fixture count, and household needs.

Step 1: Climate Zone

Groundwater temperature affects how much heating your unit needs to do. Colder climates require higher BTU ratings.

Step 2: Household Size

This helps estimate simultaneous hot water use patterns.

Step 3: Hot Water Fixtures

Select all fixtures you might use at the same time during peak demand (morning showers, dishwasher running, etc.).

Step 4: Preferences

Gas units typically deliver higher GPM for whole-house use. Electric works well for point-of-use or smaller homes.

Your Tankless Water Heater Requirements

- Required Flow Rate (GPM)
- Required BTU Rating (for gas units)
- Required Power Rating (for electric units)

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Why These Numbers Matter

GPM (Gallons Per Minute) is the flow rate your tankless unit must deliver to supply all your fixtures at once. Too low, and you'll experience temperature drops when multiple fixtures run.

BTU (British Thermal Units) measures the heating power needed to raise your incoming groundwater to 120°F. Colder climates need higher BTU ratings to achieve the same GPM.

Always round up slightly when choosing a unit - it's better to have a bit of extra capacity than to run at 100% constantly.

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