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pex tubing

BOB_22BOB_22 Member Posts: 16
I have a few questions concerning pex tubing. I want to install under floor pex in my bathroom. I know I need an oxengen barrier pex. Should I stick with Wirsbo? I read about Safelink as a good product. Does it compare to Wirsbo? Also, am I correct in assuming when you speak of 1/2" pex, you are referring to OD? My last question is, once I figure my heat loss for the room, how do I apply it to the size and amount of pex to be installed. Thanks in advance to any replys.


  • Ken_8Ken_8 Member Posts: 1,640
    A few minor discrepencies..

    Depending on what the source of the radiant sub-system is to be attached to, you may not need O2 barrier tubing.

    Most plumbing/heating tubing is measured by I.D. Most A/C tubing is measured as O.D.

    The maximum output I ever heard of for a radiant floor "panel" is 50 BTU's per S.F.

    A "micro" tube system may be the direction you want. By using much smaller tubing (and more of it) the same results can be achieved. I have designed and installed a radiant panel from 1/4" copper tube. The O.D. of which is smaller than any plastic or rubber based tubing that I know of.

    The thermal transfer rate of copper is substantially higher than PEX. However, that can be a deisgn problem when long runs are required.

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  • Steve WhitbeckSteve Whitbeck Member Posts: 669

    why not use fin tube under the floor instead of PEX tubing.
    I have used both and both have their app's.
    What is your heat source??
    If you have baseboard heat now then I would suggest the bare fin tube mounted just under the floor. No need for a mixing or tempering valve.
    If you have infloor heat then just add the tubing and radiant panels.
  • hrhr Member Posts: 6,106
    Be interesting to see copper

    in slab, modeled. I too have heard that due to it's excellent conductivity pex at a thermal conductance (btu/hr.*ft*°F) of 0.237

    copper L at 223.

    As such, some claim copper would dissapate all it's heat quickly in the first part of the loop leaving temperatures to cool near the end. Like the 1000' pex loop :0

    Would this mean copper loops of 1/2" would need to be less than 100"? Less than 50'?

    I've tried copper in ThermoFin and the heat transfer "speed" is almost instant. With 130° F water the copper was too hot to hold within a minute. Although these were only 40' loops in an exposed radiant ceiling.

    I suspect copper encased in concrete would show different results. Any numbers in the old IBR copper radiant designs?

    Next one would need to address the effects, long term, of concrete and copper. Many, many variables to consider from area to area, concrete plant to concrete plant. Flyash, the nemesis of copper, sometimes, can be mixed up to 80% (portland replacer) for warm weather workability of concrete. This could haunt copper/ concrete compatability.

    In my lifetime :)

    hot rod

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  • BOB_22BOB_22 Member Posts: 16
    pex tubing

    I think I gave the wrong impression from the replys that were given. I plan on installing pex in plates do to a recent renovation that caused me to replace the existing ceiling in my living room below the upstairs bath. After reading Dan's books on Pumping Away and Primary/Secondary Pumping, I saw how taking a heat loss of the building would apply to regular forms of radiation. I want to know how to apply heat loss calcs to radiant applications.
    I have a WM eg45 boiler. I use it to supply steam (single pipe)heat right now, but plan on changing over to hot water after the winter. I want separate zones upstairs and down This is the first step due to the open ceiling and walls. Other steps are yet to come.
  • jp_2jp_2 Member Posts: 1,935
    limiting factor

    hot rod, it seems to me that the limiting factor here is how fast the heat can move through the slab. it might jump right out of the copper but slows to a crawl through the slab. so the end result has it looking not much different than pex.
    have yet to prove this on paper but my assumption to this point.
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