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PEX growth vs a heat exchanger

Gary Jansen_4
Gary Jansen_4 Member Posts: 77
I have a project that involves doing some pool heating off a boiler system via a heat exchanger. The boilers and buffer tank are in the basement of the home, the pool heat exchanger is mounted in a pump room behind the pool. I have run 150 feet of 2" barrier Pex's from basement to pool room. The PEX tubing (supply and return) are a factory assembly, encased in a black corrugated sleeve that contains the 2 PEX tubes, as well as a heavy urethane foam insulation. This assembly is buried 4 feet underground from where it exits the basement wall, to where it enters the pump room wall. I started to pipe up the heat exchanger this weekend, adapting from the 2"PEX to 2" copper, and then on to the heat exchanger. As i looked at the installation, I became concerned about the growth and expansion of the undergound PEX, as well as the copper in the pump room.
I'm trying to figure out where the expansion will take place. Inside the basement. I'm not too worried, piping there is suspended on hangers, plenty of room to flex. But in the poolroom, the supply side will have 10 feet of copper, including 3 elbows, the return will have 5 feet of copper and 2 elbows. At this point I had planned on mounting the copper on strut with cushion clamps.

At this point in time, it is 50 degrees outside, and in the pool room. Boilers will be supplying 160 degree water once system is running.

Do I need to worry about where the 150 of PEX is going to grow to? Will I be putting excessive pressure and torque on my copper (soldered) joints? Or stressing the heat exchanger ?

Your thoughts, please.
Thanks, Gary


  • Gary Jansen_4
    Gary Jansen_4 Member Posts: 77
    I am considering connecting to the heat exchanger with braided stainless steel flex connectors. probably 18" long. Is the rubber/neoprene used in the SS connectors considered a oxygen barrier?
    Thanks, Gary
  • Jamie Hall
    Jamie Hall Member Posts: 22,187
    On the expansion. It surely will expand. At both ends, since the ground sleeve effectively anchors it. It would be best if you could arrange a loop like a U at both ends, or at the very least an unrestrained long sweep 90 degree bend with a few feet on either side.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • GroundUp
    GroundUp Member Posts: 1,769
    You must have a heck of a boiler in the house to utilize 2" pex! As far as expansion goes, are the ends (house and pool house) going to be vertical or do they terminate horizontally? If this is Insulpex or Rhinoflex with the pex physically bonded to the foam, and the foam bonded to the outer jacket, expansion is moot. The ground and jacket holds it all together except for maybe a fraction of an inch at the ends after you give it a hard anchor, like regular unistrut clamps instead of the hydrosorb style (just the end, for an anchor). L copper has an expansion coefficient of .00804 so 10 feet of straight pipe at a 110 degree differential would grow just under 1/8" but you say there are elbows in it so that will depend on how it's piped to determine actual expansion between the HX and closest elbow. Long story short, there will be some give in it and expansion is nothing to worry about if you lock down the HX and let the copper float. A simple swing joint will make up for almost any expansion you can throw at it with only a 10ft run.

    As long as you have your pex ends anchored, and your HX anchored, there is no expansion concern for a sweat joint
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,386
    Don't forget about 'bonding', not grounding, bonding (equipotential plane).
    You don't want to introduce any stray voltage into that pool, now that your basically connecting the pool to the house.