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Discussion Starter · #1 · (Edited)
I am helping with a project this weekend that includes roughing in some new plumbing. (New piping for first floor bath; new pipes through walls up to second floor bath in wall that will only be accessible while working on first floor bath).

We have CPVC for it that has been sitting in the basement for a year or so, but reading up on the installation I am a little concerned on whether we should be using PEX instead. Notably, I did not realize the linear expansion of CPVC was so high and the pipe would basically be expanding and contracting by inches if you run hot water and then let it cool off.

After looking at code and reading a manual from CPVC manufacturers, it looks like you need to add "expansion loops" which basically absorb this expansion by bending the pipe, even for short runs like 20 feet. This adds significant complexity to the system. Worse, intuitively, this seems like it significantly changes the stresses on the joints every time there's a hundred degree change in temperature, i.e. whenever you run the hot water and then let it cool off.

Between that and the increased number of joints (i.e. potential failure points) in CPVC, I am wondering if we would be better off to use PEX?

I dislike tossing hundreds of bucks worth of pipe (Will Lowe's take returns after two years?) but reliability and not having a problem in the inaccessible wall behind the tub enclosure are more important.

Am I worrying over nothing, or missing something basic? Any tips?
 

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Discussion Starter · #2 ·
OK, it's not a hundred degrees every time, but still, it seems like a lot of expansion and stress on the pipe.

Am I worrying over nothing? In practice, are expansion loops regularly used in residential CPVC installation, in any run over a certain length?
 

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If memory is correct CPVC expansion is 4 inches per 100 foot. Most will occur on the hot side. The trick to good CPVC install is to allow for the expansion. That means do not butt it up along a joist. So there is no room for movement.

I would suggest you read this over and understand it.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwiWgoyD54rNAhULKlIKHQV5AnwQFggdMAA&url=http%3A%2F%2Fwww.charlottepipe.com%2Fdocuments%2Ffgg_tech_manual%2Ffgg_tech_man.pdf&usg=AFQjCNFGqSVaE3Zh-PHMUjMvQJm2Fs5LsA
 

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I have only installed CPVC a couple times so I can't really comment on the product.
I will say that pex is used by all the local guys here. CPVC never caught on...

One light commercial job (assisted living bldg) I used it on, we broke some branch lines because of expansion and installation error. The manufacturers have researched their product thoroughly to protect themselves. So, if you follow their install directions you should be okay- we didn't. We treated it like the copper pipe we were used to.... this was about 10 yrs ago
 
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