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Plumbing in the Home/Thermal expansion tank & pressure regulator


In last 10 years I went thru 4 hot water tanks. I have coverage now thru Dominion to replace tank, but before he will change tank, I need therm exp tank and press reg. He says water pressure coming into condo is 100psi and that could be what is blowing out the tanks. Could this be correct?

Hi Don,
The "standard" that plumbing equipment is designed to is 80 psi.  100 psi calls for a regulator to bring it down to meet current standards.  That being said, 100 psi is not all that high and shouldn't really be a big problem.

Water pressure is rarely "static" and varies throughout the day and night depending on demand on the overall delivery system. It will usually peak in the early morning hours due to low demand.

A thermal expansion tank is a good idea. After you use hot water it is "replaced" with cold water into the bottom of the tank. This triggers the thermostat to light the burner or turn on the elements to bring it back to the holding temperature that is set.  This water is now being heated in a "closed" system since you are no longer drawing off water. Heating water cause it to expand. This can drive the system pressure well over 200 psi for a short time and THAT is not good.  The thermal expansion tank, as the name implies, compensates for this and can save a lot of problems. I standardly include them in my installations.
Good Luck,

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Dana Bostick


Pretty much any residential plumbing questions. For "item specific" details such as a specific model of fixture, I will need to research and there may not be any useful information available. Note: I live and work in Southern California. We do not, as a rule, use hot water or steam heating systems, oil fired boilers or private water wells so my knowledge in those areas is pretty limited. There are others here on AllExerts that can probably answer those questions better.


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