Hi everyone! My first post, and maybe many more to come.

I live in a typical condominium, in L.A. County. Built around 1980. I am installing a Whirlpool Gas Water Heater. The book recommends installing a thermal expansion tank if i have a "closed system". There is no such tank in the existing system. What is a "closed system"? How do i know if i have a "closed system"? Thanks for the help!

when your water heater heats a tank of water, that pressure in the tank will rise as the water increases in temperature and expands.
that pressure/expansion has to go somewhere. it will go right back into the water main and out to the street where its effects will be minimal.
if you have a check valve (one way valve) at the water main the pressure/expansion can not go anywhere so it will blow the relief valve on the water heater.

quote; blow the relief valve on the water heate

The word "blow" makes it sound dangerous. A more reasonable statement is "make the relief valve leak".

Thanks Packy! That answered my question.



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