Expansion Tank Size Calculator
Who it's for: Plumbing service technicians, installers, and inspectors.
Calculator Inputs
Quick Summary
- Built for: Plumbing service technicians, installers, and inspectors.
- Key outputs: Estimated thermal expansion volume, Minimum expansion tank size, and more.
- Use this page for early planning estimates before final code and manufacturer verification.
Inputs
- Water heater volume
- Incoming pressure (psi)
- Relief valve set point (psi)
- Cold and hot water temperatures
Outputs
- Estimated thermal expansion volume
- Minimum expansion tank size
- Code-verification reminder
How this calculator estimates results
- Converts stored water volume from gallons to liters and applies a simplified thermal expansion fraction.
- Estimates expanded water volume across entered cold-to-hot temperature rise.
- Applies a pressure factor to approximate required tank acceptance volume and maps to common acceptance classes.
Cross-check assumptions with Water Heater Size Calculator for a more complete planning workflow.
Common ranges and tips
- Measure real static pressure at the heater location before final equipment selection.
- Closed systems with PRV/check devices typically need expansion control, verified locally.
- Always confirm final tank selection with manufacturer sizing charts and installation requirements.
Related Calculators
FAQ
No. This calculator is a quick estimate and must be validated with the selected tank manufacturer sizing method.
Available pressure differential affects how much expanded water the tank can absorb, changing required acceptance volume.
That reduces effective pressure margin and can increase required acceptance volume significantly in this estimate model.
Review carefully in closed systems, after pressure changes, or when nuisance relief discharge appears, then verify with qualified professionals.
Disclaimer: Use results for planning only. Final design and installation decisions must follow local code and manufacturer documentation.
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