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

[avc8130]

I helped a buddy replace a run of baseboard in his basement. It was an interesting loop. The supply and the return came in through a wall from the boiler room. The supply was on the bottom and went through the fin tube. We then looped back and the return ran through the baseboard cover and back out on top of the supply. No big deal, pretty standard.

My buddy wanted to use a length of Pex for the return as it was 20' and it saved about $40 over the cost of 3/4 copper. So I cut it to length and installed it.

We fired up the zone. The moment the 190F boiler supply hit that Pex it expanded ~3" in length and wouldn't fit in the register cover any more.

How do people work with this stuff? How do you account for 3" linear expansion on a straight 20' run?

ac

 

[BoilerMan]

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

 

[avc8130]

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

Yeah, I know the answer now. Not happy. My perfect job turned to pooh. I'm not sure the exact type of Pex we used. It was o2 barrier. We cheated and used a Sharkbite on each end to go from copper to pex in 1 step.

I've never been a fan of pex. I guess there is savings, but every time I look at it, the fittings still cost a fortune and the job always looks terrible when it is done. This experience just solidified my opinion even more.

ac

 

[Vizsla]

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.

 

[avc8130]

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.

Hmm...didn't really get any instructions with the straight single length of tube.

I'm done with this stuff for anything but underground use. If it is worth doing once, it's worth doing right. Copper or black pipe for me.

ac

 

[Vizsla]

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".

 

[BoilerMan]

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

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

 

[MarkW]

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.

 

[arbutus]

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.

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?

 

[MarkW]

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

 

[heaterman]

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.

 

[kopeck]

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

 

[MarkW]

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

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.

 

[avc8130]

Yeah, it was 02 barrier. We wound up zip tie-ing it along the way into a lazy "s" behind the baseboard cover. It did break a pipe off the wall outside of the room.

Like I said, I guess this stuff has its place, but I doubt it's place will be in my house much.

ac

 

[arbutus]

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.

 

[Boil&Toil]

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?):

 

[Karl_northwind]

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.