Can someone please explain to me expansion tanks as they relate to radiant floors with pex tubing.  I know that expansion tanks keep the system from exploding when the rise in temperature causes increased pressure.. I'm wondering if expasion tanks also relieve pressure in the pex tubing???  I know that most the stuff I read said to put a "loop" in the tubing for expansion but wonder how it is possible when I see one of the following two scenarios:

1) Pex tubing placed in cement (or gypsum) and the pex seems to come right out of the floor and into the manifold.
2) Pex tubing in an above floor based system like "Climate Panels" in which the also seem to come right out of the floor and into the manifolds.

I can see "expansion loops" in below joists installation easily done but what about these other two?  Does the expansion tank do the "heavy lifting" here also for the pex?

Expansion Tanks give the water a place to expand into when it's heated so system pressure doesn't elevate excessively. Water is basically incompressible, so when it expands, pressure increases very rapidly if we don't have a place for it to go.

Expansion loops are specifically for the expansion and contraction of the PEX itself as it heats and cools. In concrete it's a non issue because, in basic terms, the PEX can't move. In over the floor panel systems I prefer to use a PEX-AL-PEX to limit any noise potential but in many systems it's not a large concern for a variety of reasons. Climate panel, for example, usually has short loops of small pipe seated in silicon so while it may move a little it's not generally enough to cause noise problems.

THANKS!

And welcome back! I used to follow you a few years back when you were with a partner running your own place. I love (and trust) the vast knowledge you have! I even tried to hire you for the side job (actually my own place) that I'm doing. At the time you were too busy. As you can tell, I know little about this field but find it fascinating. Thanks for contributing to my knowledge and others.

Thanks, User Name, I remember you fondly too