Expansion on heat-pex piping.

Allislandradiant

I was looking for some input from the group how they handle expansion on long runs of heat-pex tubing. This is for a snowmelt job that has a run approximately just under 100ft of 1 1/4" from the point of exit of the house to a 4 loop manifold. I ran the 1 1/4" heat-pex tubing in a 3' PVC conduit for the total run. Every time the snowmelt goes on the piping in the basement expands approximately 5"-6". I used expansion fittings for my connections. Just concerned over time they may leak because of the movement of back and forth. Spoke with Uponor and they told me not to be concerned, but we all have heard that before.

hot_rod

No way to stop that expansion movement. As long as it is not stressing any fittings on either end, let it move. Sometimes an expansion loop is used, but they look funky.

Allislandradiant

I remember Uponor used to make a fitting to handle this, but no more. I am just concerned with Uponor expansion fittings putting stress on them.

hot_rod

Yep, choices are to lock it solid, like encased in concrete
Or leave room for it to safely move.
A swing ell like you would use on threaded steel steam piping to allow movement may work, but 6" is a lot to accommodate

Allislandradiant

Ok, thanks for your input. 

ethicalpaul

Dumb question: when you "lock it solid like in concrete" what happens to the expansion then?

Jamie Hall

ethicalpaul said:

Dumb question: when you "lock it solid like in concrete" what happens to the expansion then?

You wind up with a lot of compressive stress in the pipe -- which shouldn't be a problem -- which shows up as a very slight increase in wall thickness -- which also shouldn't be a problem.

Now if there is a short section somewhere which isn't restrained... if the pipe decides to slide, which could happen, it will buckle and ruin your whole day.

hot_rod

At the PPI website they show how to calculate an expansion arm. This may be cleaner than a U shape expansion loop?

Enter the tube size, length and temperature change and it shows how to build the arm

Ironman

This is one reason that we use PEX-AL-PEX when provision for expansion is not available. It only grows about 1” per 100’ @ 100* temperature rise. Very similar to copper. With PEX, it’s about 12 times that.

hot_rod

Ironman said:

This is one reason that we use PEX-AL-PEX when provision for expansion is not available. It only grows about 1” per 100’ @ 100* temperature rise. Very similar to copper. With PEX, it’s about 12 times that.

Can you still find 1-1/4 PAP
and fittings?

Allislandradiant

Next time I will use fusion plastic pipe. That’s what we used inside. Nupi is the manufacturer.