Thermal expansion tank on supply side

[Theydarg]

Im not quite following the reason/logic for placement of TET on cold water/supply side. I understand the principle of thermal expansion from heating but I did not think that this additional pressure could move backwards in the system…i.e. towards the supply. I had thought that all additional pressure would push toward the hot water side due to check valves in the water heater? Could someone please educate me a bit more on this. Thank you

 

[WorthFlorida]

Water heaters have a thermal block, not a check valve. Cold water pressure is always more than hot water side When water is running. When the water expands, both hot and cold pressure builds. Expansion tanks use a bladder and hot water will shorten its life.

At my son's house with about a 12 year old electric water heater, the T&P valve started to weep water. About a cup a day during the night and daytime when no water was used. With a tattletale gauge the pressure was getting well over 100 psi. We added an expansion tank on the cold side and the problem went away. Replacing the T&P would might have stopped the weeping but the problem was too much pressure. He already had a water claim when the ice maker water line blew when no one was home.

 

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[Jeff H Young]

basically the cold side and hot side of your piping system is the same. Theydarg you gotta understand that right ? nothing to educate you there any piping system thats interconnected will have the same pressure or close to it a thermal expansion tank dosent do a thing while the water is running