Water Heater Expansion Tank

What Is it and why do I need it?

An expansion tank is a metal tank connected to a building’s water heating appliance designed to accommodate fluctuations in the volume of a building’s hot water supply system. These fluctuations occur because water expands in volume as it gets hot and loses volume as it cools.

Expanding water volume in a closed system can create dangerously high-water pressure. As water is forced into the tank by expansion, it compresses air contained inside of a rubber bladder. Air is used as a cushion because it exerts less force on its container than water, which cannot be compressed.

The function of this bladder is to prevent air from becoming absorbed into the water, a process that could cause the expansion tank to lose its ability to act as a sort of shock absorber. If, over time, the bladder begins to leak some air, a Schrader valve, identical to the fill valve found on bicycle and car tires, can be used to add more air.

Where should mine be and what might it look like?

Expansion tanks are considerably smaller than water heaters, usually holding about two gallons in residential systems, although tank sizes vary in relation to the water volume of the hot water supply system they serve. The design pressure for which a tank is rated is marked on a label on the tank, commonly 150 pounds per square inch (PSI) for a residential tank.

Expansion Tank Is a small tank attached to the hot water source. Designed to absorb pressure differences.

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