When running PEX-A through joists for a boiler heat run, what do you do to combat expansion noise?

wmarler

I recently replaced a long section of copper pipe that was mounted under my joists with oxygen-barrier PEX-A that I ran through my joists, to gain that inch of headroom when I close my ceiling (future project). I didn't realize how much the PEX would expand under the high temps of the water flowing through it -- it's quite a bit. When cold the PEX is snug, and when it's not cold, the PEX droops significantly. I'm hypothesizing that the series of clangs that I hear when the system heats up is the sound of the PEX expanding -- the PEX sticks to the joists at first, then pops as it as it overcomes the static friction, causing shockwaves to reverberate through the loop, which is still mostly copper. The PEX passes through about a dozen joists, and when the loop heats, the banging/clanging lasts a good 2-4 minutes.

I was thinking I'd line the holes in the joists with a material that the PEX would slide cleanly against -- maybe Teflon, or something else. Does anyone have any experience with this, and can give me any product recommendations?

This just occurred to me as I typed out my questions so I haven't done it yet: would putting tube clamps every 16-18" during the portion of the run where the tubing is between bays seems be helpful? They're not needed when the water is cold, the pex supports itself no problem with just 2-3 clamps over a 20' span. But when the water is hot there's noticeable sag. Is maybe the weight of the tubing (+water) in that section putting tension on the tubing, acting as a force to pull the PEX through the joists in addition to normal expansion? Or am I overthinking?

Thanks in advance

hot_rod

At 210 that Pex will be like a spaghetti noodle! Why so hot?

You can make a 180 loop or a complete circle in the pex to accommodate expansion. Look up the Uponor or other pex brands installation manuals.

Plenty of isolators for pex, Sioux Chief has a bunch of options.

wmarler

At 210 that Pex will be like a spaghetti noodle! Why so hot?

Trial and error -- the boiler has a high set point of either 180°F or 210°F, and at 180°F our house wouldn't warm up on the coldest days.

hot_rod

No doubt if that tube cools to room temperature then see 210 it’s going to do the Mambo. Can you run it on an outdoor reset control to limit the wide swings?

Rich_49

Straps , ODR and expansion loops