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Fixing wires - How tight is too tight for PEX?

Torsten
Torsten Member Posts: 3
edited May 2016 in Radiant Heating
Just curios if it is possible to damage PEX when tying it to rebar using these Uponor Fixing Wires and tying it it to tight ?

On one hand, the PEX needs to be tamed at turns, and also held closely in place to not float up towards the surface and potentially be cut when doing control joints. On the other hand, could it be cut / damaged by tying the fixing wire too tight? I have seen guys use pliers to turn the fixing wire to be really really tight.

Comments

  • hot_rod
    hot_rod Member Posts: 16,274
    If the wire is cutting into the outer layer of the tube, it is too tight, I think.
    Many radiant pex brands have an EVOH outer layer, very thin. damaging that layer could lead to O2 ingress.
    Really the tie is mainly to prevent the tube from floating, not to prevent it from sliding .

    Allowing some play in the tie may help get the tube up into the pour. Unless you lift or support the mesh, the tube ends up in the very worse position, at the bottom of the pour :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Mark Eatherton
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    edited May 2016



    As HR said, not so tight that the tubing can't move, but tight enough to do the job.

    I have had occasions to open up a slab after the fact that an electrician had "Discovered" our tubing for us. It was a slab ob grade pour. The tubing was distorted from the ties. The barrier hadn't been violated, but there were obvious pinch marks on the exterior of the tubing. I do not believe that the Europeans allow the tubing to be tied to metal with metal.

    I am not aware of any massive failures associated with this method of tube fixing.

    Although a pain in the thumbs, I prefer the use of cable ties. In fact, when I did my daughters sidewalk (curved) I used some of that "Snow Fence" for the mesh, and nylon ties. NO metal in contact with the tubing. I affixed the mesh to the ground using landscaping stakes (plastic, Ortho) and from what I hear, it held quite well during the pour. I intentionally wanted the tubing as deep as possible, because this is also a reversing system that can take advantage of the solar and ambient energy to be harvested for use as a DHW pre heat.

    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • ron
    ron Member Posts: 217


    I intentionally wanted the tubing as deep as possible, because this is also a reversing system that can take advantage of the solar and ambient energy to be harvested for use as a DHW pre heat.

    to use solar energy for DHW preheat, why should the pex tubing be as deep as possible? If you could provide links to the technical reasons for that i'd be interested in learning about it. thanks.
  • SWEI
    SWEI Member Posts: 7,356

    Although a pain in the thumbs, I prefer the use of cable ties.

    Agreed, and I leave the tails on them just like you did. Less work, and why throw away some free reinforcement?
    when I did my daughters sidewalk (curved) I used some of that "Snow Fence" for the mesh, and nylon ties. NO metal in contact with the tubing.
    Clever hack. Non-metallic reinforcing provides chloride ingress immunity -- big deal in coastal areas. Here's the high-tech version.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    Ron asked:

    to use solar energy for DHW preheat, why should the pex tubing be as deep as possible? If you could provide links to the technical reasons for that i'd be interested in learning about it. thanks.

    Ron, unless the tubing is on some seriously substantial support system, it's going to end up on the bottom in most cases anyway. No real scientific reason, just a gut feeling and mimicing real world experience. You will note the sensor well in one photo near the manifold box. It will contain the slab sensor used to dictate operation of the SIM and energy recovery programs. I will not allow it to be drawn below dew point, which here in Colorado is fairly low. I could "make" water, but am worried about the accumulation of condensate slime. If I'd have thought about it sooner, I could have had the cement plant throw some copper sulphate into the mix, and then I could have generated enough water to maintain plant life for the Xeriscape plants along side of the sidewalk for free :smile: I don't think the landscaping would have appreciated the copper sulphate tho.... Trade offs in every corner...

    Extraction will be a 2 stage process. Direct off the slab, through a plate heat exchanger when differential is adequate, and 2nd stage is a vapor compression heat pump. Heating is done direct via modcon through plate heat exchanger to the slab. The whole shebang will be controlled via an ENV PC based control system. (Google Climate Automation Systems for more information).

    My ultimate hope is to show that we can harvest more energy than the SIM system uses for keeping the sidewalk clear, and create more SIM sales for our manufacturers. There will be times during the seasons that we can actually harvest the night time ambient energy from the slab as well. Having the tubing at the bottom of the slab will lessen short cycling of equipment due to mass storage tendencies of concrete.

    Mechanicals begin in earnest this fall. Would have started sooner, except that we had to establish a baseline for consumption (brand new home) to have something to compare to.

    I am soliciting participation by hydronic equipment manufacturers, including Caleffi, Grundfos, Taco, and others. ENV is donating the programming. I donated the insulation, tubing, mesh and S&R lines between the slab and mechanical room. All participants will be named in the final executive report of findings. The Environmental Defense Fund is also interested in our findings.

    ME


    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    SWEI said:

    Although a pain in the thumbs, I prefer the use of cable ties.

    Agreed, and I leave the tails on them just like you did. Less work, and why throw away some free reinforcement?
    when I did my daughters sidewalk (curved) I used some of that "Snow Fence" for the mesh, and nylon ties. NO metal in contact with the tubing.
    Clever hack. Non-metallic reinforcing provides chloride ingress immunity -- big deal in coastal areas. Here's the high-tech version.


    Cool stuff. We really didn't need any "reinforcement" for her slab, hence snow fence for tying to. Bet mine is less expensive :wink:

    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.