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Calcimator

Water Heater Size Calculator

Determine the right water heater tank size or tankless GPM based on household size, usage patterns, and water temperatures.

Inputs

people
°F
°F
$/kWh

Results

Tank Size

75 gal

Peak Hour Demand48 gal
Tankless GPM Needed6 GPM
Temperature Rise70°F
Est. Annual Cost$996

Tank Size

75 gal

How to Use This Calculator
  1. Start by filling in the input fields below. Results update instantly as you type, so you can experiment with different values to see how they affect the outcome.
  2. Household Size — Number of people in the household. Accepts values from 1 people to 10 people (default: 4 people).
  3. Peak Hour Usage — How heavily hot water is used during the busiest hour. Choose from: Low (staggered showers), Medium (typical morning), High (simultaneous use). default: 2.
  4. Incoming Water Temp — Temperature of the cold water supply (varies by region and season). Accepts values from 35 °F to 80 °F (default: 50 °F).
  5. Desired Hot Water Temp — Target hot water temperature at the tap. Accepts values from 100 °F to 160 °F (default: 120 °F).
  6. Electricity Cost — Local electricity rate in dollars per kilowatt-hour. Accepts values from 0.05 $/kWh to 0.5 $/kWh (default: 0.13 $/kWh).
  7. Once all inputs are set, review your results in the Results panel. Here's what each output means:
  8. Tank Size — shown as a numeric value. This is the primary result of this calculator.
  9. Peak Hour Demand — shown as a numeric value.
  10. Tankless GPM Needed — shown as a numeric value.
  11. Temperature Rise — shown as a numeric value.
  12. Est. Annual Cost — shown as a dollar amount.
  13. Explore the related calculators below if you need deeper analysis or want to approach this topic from a different angle.
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