Heat expansion of PEX tubing

General Questions
#1

Several years ago, we had a second floor put on our house, and the plumber used PEX tubing for nearly all of the plumbing. For the most part, I’m quite happy with it. The PEX that feeds the forced-hot-water baseboard heat is stapled to the underside of the first floor’s joists, then snakes through the back of a first floor closet to feed the convectors in half of the second floor. When that zone calls for heat, the hot water flowing through the tubing causes it to expand, it looks as if there is a 50% increase in length given the “S” shape that the tubing assumes. As it expands, it creaks and pops through the staples under the floor, and contorts itself through the walls, making a surprisingly loud crackling sound as it does so.

My wife has “had enough” of the noise, and has given me the mission of “making it stop.” I could attempt to switch the PEX to copper, but it is quite a long run and I’m not keen on the investment, given today’s copper prices.

I have seen (both in the stores and on television) a newer version of PEX that has an aluminum tube along with the plastic. The price seems to be comparable to “regular” PEX, does the aluminum PEX have similar expansion issues as the old style, or does it come with its own noise issues?

#2

50% (10’ expands to 15’) didn’t pass the sniff test so I did a quick Google and found this spec sheet/ installation guide (PDF).

Rather than a total rework, you might be able to just redo it with expansion points and loose staple it so it can move peacefully.

#3

What do you mean ‘stapled’? The PEX installations I have seen always involve plastic nail-on clips and some times other fasteners/guides for specific cases that are designed for PEX. These fasteners definitely allow movement.

We have built quite a few homes utilizing PEX for supplementary heating, usually in concrete slabs. Several installations have been under tile in specially developed plywood substrate, or under the floor in joist-space panels. These applications are pretty much noise-free from my experience. PEX in general I would describe as generally quieter than copper; I assume because it is so flexible.

There is almost certainly something not right about your plumbing if it is really that noisy. I know trades almost always are critical of another’s work, but a second and third opinion is definitely a good idea. I am sure you could find some Plumbing and heating forums that would have a number of knowledgeable pro’s willing to comment on your problem.

I really doubt replacement with copper is the answer.

#4

This doesn’t sound right. Something else is going on. PEX certainly doesn’t expand that much with heat (or contract that much with cold). You might be in a situation where the actual thermal expansion pushes the loose pipe out into a curve?

Of course you are the one there and have the best information, but it sounds to me that additional study to understand the problem will help. PEX does expand/contract, so clips that allow for that are needed, but that should be part of any installation.

I haven’t heard of PEX with an Al. tube. Not sure what the advantage is. Is the concern that PEX will split? How flexible is this? How easy is it to connect? I don’t see what the advantage of such a combination would be.
Good luck

#5

Projammer, expansion points and loosening the staples might be the solution. The plumber* stapled the PEX at every joist, and he truly whacked them down solidly, so the tubing is rigidly held every 16" down a 35’ or so run. When the tubing heats up (remember, it’s for baseboard heat, there’s some pretty hot water flowing through), it deflects 4" out of alignment between every joist/staple. The noise of the tubing trying to flex through the staples really is quite loud, I would imagine the flooring above the joists acts as a large sound board to amplify the noise.

FluffyBob, the noise we are hearing isn’t water flowing through the tubing itself, it is the noise of the tube expanding through the fasteners, it is a long series of squeaky-snaps from the plastic tubing rubbing against the plastic clips. What I referred to as staples could easily be called plastic nail-on clips. I am very well versed in electrical work, they remind me of very large co-ax cable staples - one nail to the side of a large half-circle that encompasses the tubing. You said there are guides and other fasteners, do you have a good link for a supplier?

*I can’t say many good things about him, I was not at all satisfied with his work - neither was the building inspector, who made the comment “wow, he was angry when he did this” when he saw some of the plumber’s, uhm, ‘carpentry’ work. A line from the plumber - “I’m going to put some nice new holes in here.” “What’s wrong with the existing holes that are lined up with the sink?” “No, you need new ones.” Not a fan.

#6

rbroome, what you describe is the exact issue - the thermal expansion is pushing the tubing into a curve between each staple/fastener. That expansion, with the tubing trying to push through the fasteners, is what is causing the noise. The PEX with the aluminum tube inside, from what I’ve seen, will hold curves and can be installed in a straight line, giving a nicer look than PEX. I believe Zurn markets it under the name “Alumicore.” I don’t know if it has a similar expansion issue as the “normal” red PEX does.
(missed edit window above)

#7

Typically, the aluminum is just to prevent oxygen from leaching through the pipe and corroding boiler components, Wirsbo (Uponer) and others use a special cross-linked poly to prevent this. It has little to nothing to do with expansion.

Another issue: often baseboard supply heat is beyond the rated range for PEX. I would definitely check the rating (should be printed on the pipe) and your supply temp. I have seen PEX pipe severely compromised (but not yet failed) by this.