Quote:
Originally Posted by photo1902
It's also required by code.
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It may be required by code, but if you have an older house that does not have an expansion tank, there are licensed plumbers who will not install one unless you demand it. Without an expansion tank, the water pressure in your tank can get so high through thermal expansion that it can damage your plumbing system. The expansion tank is more important now because water supply systems have better backflow protection and plumbing fixtures do not leak as much as before. So it is more likely that when you are using no water, the water heater will heat the water and cause thermal expansion which can result in extremely high pressure in your system. Some plumbers will tell you that the relief valve on the tank will protect you, but that is false. The relief valve is only an emergency device. All new water heater installations should have an expansion tank.