Observed arrival · 2026-09-29
Water Heater Sizing Calculator
A free calculator sizes tank water heaters by First Hour Rating and tankless units by flow at the chosen temperature rise.
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$Paid
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✦Pretty
●Pro
◎Niche
◉Human
⚑Risk
ƒJS
- For
- Homeowners comparing tank and tankless water heaters
- Worth noticing
- It separates tank First Hour Rating from tankless flow and flags when inlet water is below the DOE rating-test temperature.
Field notes
The tank workflow counts fixture uses in the single busiest hour, with editable incoming-water and heater-setpoint temperatures. Its example separates the 35.2-gallon demand estimate from the 36-gallon-per-hour minimum FHR, and warns that colder inlet water can reduce performance relative to the published rating. The page also links guides on FHR, temperature rise, and whole-house tankless sizing.
Observed signals
Read the marks
Editorial observations of this landing page, not a rating.
○OpenPublic substance visible
✦PrettyNotable craft visible
●ProPolished or operationally mature
◎NicheUnusually specific use
ƒJavaScriptBrowser-side code central
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