Water Heater Sizing Calculator (Tank)
- Peak-hour demand
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- Recommended tank
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- First-hour rating
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Federal first-hour rating chart: tank gallons ≈ peak-hour demand − recovery during that hour. Typical recovery: 18–22 GPH (electric), 40–50 GPH (gas).
About this tool
Water Heater Sizing Calculator (Tank) is a single-purpose utility on instant.tw, a free toolbox of calculators, converters, generators, and quick lookups. Everything works in your browser — nothing is uploaded, nothing is stored on a server unless explicitly noted.
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