Linear Expansion of Pex, how do you deal with it?

Well I'm guessing you already know the answer....

Don't use it within the BB cover, copper is the ONLY think I'll use on a return in the cover. PEX/AL/PEX doesn't expand as much, but takes special connecting compression fittings which are expansive, so copper wins again.

Sometimes the $40 you save will cost you more in aggravation. I may be biased though and must admit my love for copper heating work.

TS

It actually mentions this in the manufacturer install instructions. Making connections with the expansion in mind. It would be enough to compromise a push fit fitting as well.

My apologies if that sounded bad, but I wasn't being sarcastic. Just pointing out that pex actually mentions it because its a concern not found with other materials. It by no means would stop me from using it. As I do everyday. Those modular homes are all pex for the boiler system, except the fin tube and near boiler piping. Within 12-18".

Vizsla said:

Those modular homes are all pex for the boiler system, except the fin tube and near boiler piping. Within 12-18".

Click to expand...

We shouldn't go there........I've done LOTS of work in modular homes, well we'll just leave it at that. You get what you pay for.

And I too use pex on an almost daily basis.

TS

When installed in-slab, where does the linear expansion go? I want to do a slab on grade home this year with in-floor radiant.

MarkW said:

When installed in-slab, where does the linear expansion go? I want to do a slab on grade home this year with in-floor radiant.

Click to expand...

It can't expand lengthwise, it can't expand outward in diameter, so it expands inward (a little) and there are some thermal stresses left in the plastic. Not enough to worry about.
In a slab the difference in ambient temperature and heated water temperature might be a third of what fin tube baseboard runs - 60 degrees F to 100 degrees F vs 60 degrees F to 180 degrees F.






Install it outside the radiator cover and put talons or hangers every 2' max and it will look neat without sagging. 4' unsupported will make an unsightly sag.

Did you use O2 barrier pex?

That's right, I hadn't considered the reduced temps

Fact 1: Pex grows. The larger the temperature increase from room ambient, the more it grows.

Fact 2: This limits the applications which it is suitable for.

Solution: Use it in situations where "growth" will not effect the outcome of the job.

A little Thursday morning wisdom from a been there, done that guy.

I never had any any idea how much it expanded until I made a new run to a room I just finished refurbishing. 3/4" Rifeng pex, spent a small fortune on Clic clamps and used some choice words to make nice neat runs...

Put the hot water to it and it becomes a big floppy mess. Now this is all in the basement so I guess it doesn't matter but it still bugs me. I guess I would have coughed up the few extra bucks and went copper in stead if I had know. What funny is it cools down and it reverts back to it straight form.

Also, the "ease of instillation" is a bit of a myth, at least with 3/4"

K

kopeck said:

Also, the "ease of instillation" is a bit of a myth, at least with 3/4"

Click to expand...

I'm with you, there. 1 1/4" from the shed wasn't so much fun, either. I wondered if wrestling an anaconda might be easier.

Retrofit installation of half inch hepex for a bunch of radiators on the second story of our house went pretty well, along with pulling/snaking 300' runs through the joist cavities under the first floor, around all the stuff already there - wires, supply and drain plumbing, diagonal bracing.

Far less work than sweating a million pieces of copper, and a tremendously lower cost.

As a homeowner handyman, I like it.

If I do plumbing work in the future it will likely be with pex as well.

In my limited experience, PEX is most expensive to do and least satisfying to folks who treat it like pipe, and use a million fittings wile trying to make "nice neat runs." Folks at my workplace are wired this way, and it makes me nuts; umpteen useless elbows in every run. To me, the entire joy of PEX is that I just connect a line to a fitting and wend it through the house until it gets to the supply (passed on the manifolds, rolled my own for less.) For the plumbing side of things, each item supplied has one 3/4x1/2x3/4 tee, one valve, and one terminal fitting, plus some PEX to connect it all.

As for dealing with linear expansion, provide loops or offsets. I learned about those decades ago, and it had nothing to do with PEX - "Why are there these places in the paper company steam lines where they suddenly go 10 feet sideways, 10 feet ahead, and 10 feet sideways again?" Here's a loop for the neat freaks, one for the metal pipe guys (and those who treat PEX as metal pipe), and a (huge) loop for the less tidy (perhaps just not finished pulling pipe at this stage?):

www.falconstainless.com for stainless flexible connectors up to 2". pretty reasonable as these things go. I have used them for fixing similar issues on solar thermal systems that frost heave.