Expansion Tanks

Expansion Tank Sizing Guide

Expansion TankVolume (gallons)
Max. Temp Setting 150°F
Expansion TankVolume (gallons)
Max. Temp Setting 180°F
Water Heater
Size (gallons)
Static Supply Pressure (psi) Water Heater
Size (gallons)
Static Supply Pressure (psi)
40 60 80 40 60 80
40 2.0 2.0 2.0 40 3.2 3.2 3.2
50 2.0 2.0 3.2 50 3.2 3.2 4.4
60 3.2 3.2 3.2 60 3.2 4.4 10.3
80 3.2 3.2 4.4 80 4.4 10.3 10.3
120 4.4 4.4 10.3 120 10.3 10.3 10.3


Amtrol Therm-X-Span T-5 Thermal Expansion Tank 2 GallonAmtrol Therm-X-Span T-5 Thermal Expansion Tank 2 Gallon
Part Number: T-5

  • Total Volume: 2 Gallons
  • Inlet/Outlet Size: 3/4" NPTM Stainless Steel
  • Height w/o Stand: 13 "
  • Diameter: 8 "
  • Tank Materials: Steel Shell
  • Origin: USA
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Therm-X-Span T-12 Thermal Expansion Tank 4.4 galTherm-X-Span T-12 Thermal Expansion Tank 4.4 gal
Part Number: T-12
Alternate Part Number: 141-363
  • Total Volume: 4.4 Gallons
  • Inlet/Outlet Size: 3/4" MPT
  • Height w/o Stand: 15 "
  • Diameter: 11 "
  • Tank Materials: Steel
  • Origin: USA
  • Certifications: NSF Certified to Standard 61
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What is Thermal Expansion?

When water is heated it expands. For example, water heated from 90ºF to a thermostat setting of 140ºF in a 40 gallon hot water heater will expand by almost one-half gallon. This is because when water is heated, its density decreases and its volume expands. Since water is not compressible, the extra volume created by expansion must go someplace. During no-flow periods in a system, pressure reducing valves, backflow preventers, and other one-way valves are closed, thus eliminating a path for expanded water to flow back to the system supply. Hence, system pressure increases.

Thermal expansion of water in a closed plumbing system can create a number of annoying and potentially dangerous problems. These include: the build up of unusually high pressure in a system (even when a pressure reducing valve is installed); pressure surges; and the chronic or continuous dripping of a temperature and pressure (T&P) relief valve. In addition, dripping faucets and leaking toilet tank ball cock fill valves are also symptomatic of thermal expansion.

More serious problems can also occur due to thermal expansion. When dangerous pressures are built up in a water heater, internal parts may fail such as the internal flues, fittings or water connections. If a flue way collapses it can lead to the potential release of toxic gases, such as carbon monoxide into living spaces. Thermal expansion can also lead to a ruptured or distorted hot water heating tank and may void the manufacturer’s warranty.