Expansion tanks, appropriately named, are the required solution for closed potable water systems. When properly installed, the expansion tank acts as an overflow bladder and will safely contain the expanded volume of water. It is imperative that the proper expansion tank is installed based upon the capacity of the water heater tank. Furthermore, the expansion tank is required to be pressurized to match the static water pressure of the supply.

Photo Courtesy of Watts Regulator Company
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