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PEX versus copper flow resistance??

hr
hr Member Posts: 6,106
in THE MAIN WALL
it works much better for applications like yours. Plenty of compression type fittings, even baseboard ells available.

The pipe diameter has most to do with the flow rate you expect to run through it. 1/2 pex should easily move 15k btu/hr.

hot rod



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Comments

  • cdherman
    cdherman Member Posts: 1
    PEX versus copper flow resistance??

    OK, I am replumbing some baseboard radiant units currently fed with 1/2" copper. The current layout suffices in terms of comfort and performace (so don't tell me to go do a heat loss calculation).

    I checked copper prices and whoa nellie --- its time to catch the wave and go PEX.

    Figuring that 1/2" pex was pretty much like 1/2" copper, I ordered 300' of PEX with O2 barrier.

    But now I see that the coefficient of resistance (or whatever they use to describe how hard it is to push water through the pipe) is not as good with 1/2" PEX as it is for 1/2" copper.

    But there are less sharp elbows with PEX.

    My new run may be longer.....

    What is the "real world" experience. Should I go to the trouble of getting/using 3/4" pex. I dislike 5/8 (no local supplier of fittings).

    Just give your opinion -- I am not going to make a final decision on one anonymous post on the internet. But I need more info to get my thought processes rolling......
  • Weezbo
    Weezbo Member Posts: 6,231
    the pex you buy has something to do with what you,...

    want to get accomplished.

    He Pex and RehauO barrier are two good products that you can use with heating applications.

    Aqua pex and Rehau potable are good products for potable water.

    pex is "slippery" as surfaces go and because a run doesnt necessasarily Need fittings a great deal of restriction in flow is basically non existent. therefore you can safely replace 1/2" copper with 1/2" pex without incuring any penalties. one thing though you cannot arbitraily use pex for any liquid. or gas. dont even think of using it for line sets or natural gas. while there are pex products that may be used for nat gas they must be Rated for it and used only within the applications described by the manufacturer and with only the correct fittings by that manufacturer and only when it is approved for use by the AHJ in your area.

    i will see if i can find some numbers for temps and flow. to my knowledge PEX X X has had some issues in some climates when burried underground and used for natural gas. hope that helps.
  • Scott Gregg
    Scott Gregg Member Posts: 187
    Less fittings, use bend guides

    With the Rehau PEXa you can also use bend guides instead of 90* elbows. This helps alot. If you use the "Everlock" fittings on it, they are considered full port and have a negligible pressure drop comared to the standard crimp. They would also reduce the chance of leaks to 0.

    This is getting pretty popular in VA compared to copper for retrofit jobs like yours.
  • John Barba_2
    John Barba_2 Member Posts: 92
    This chart should help...

    Gives you a pretty good idea of what you can do with 1/2" hePEX. Find how how many feet of BB you have on a loop, then find the feet of head per foot of hePEX (don't count the element), then multiply that by the length of the PEX loop and you have your head loss. Then find a circulator that'll do it. We have another chart for MultiCor (Pex-Al-PEX) if you want it. Lemme know. Hope this helps...

    JMB
  • Ron Schroeder
    Ron Schroeder Member Posts: 995


    Hi John,

    I noticed that the allowed flow in feet per second is much over the usual 4fps??????
  • John Barba_2
    John Barba_2 Member Posts: 92
    HI velocity PEX

    PEX can handle much higher velocity can copper can. Limiting concerns would be the copper element and any other copper piping in the system. As a result we're looking at about 25,000 BTU's on 1/2" and maybe 35,000 on 5/8", unless you get cute and split the loop or even use a manifold and do baseboard "home-runs." Now we're talking!
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