Thermal Expansion Tank Sizing
Size expansion tanks per plumbing code
Expansion Tank Results
Recommended Tank Size
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Minimum Capacity
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Water Expansion
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Expansion Rate
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Acceptance Factor
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Standard Tank Sizes
| Tank Size | Heater Capacity | Max PSI |
|---|---|---|
| 2 Gallon | Up to 50 gal | 40-60 PSI |
| 4.5 Gallon | Up to 80 gal | 40-80 PSI |
| 10 Gallon | Up to 120 gal | 40-80 PSI |
| 14 Gallon | Commercial | Up to 150 PSI |
Installation Requirements
Why Required?
When a pressure reducing valve (PRV), check valve, or backflow preventer is installed, the system becomes "closed." Water cannot expand back into the main, so pressure builds during heating.
Without an expansion tank, pressure can exceed T&P relief valve rating, causing:
- Frequent T&P valve discharge
- Premature water heater failure
- Fixture and valve damage
Installation Notes
- Install on cold water supply to water heater
- Pre-charge tank to match supply pressure
- Support tank to prevent stress on piping
- Install with shutoff valve for service
- Vertical or horizontal mounting OK
- Keep diaphragm above water level when possible