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Hydronic Radiant Heat – Wall Anchor Dangers? (Ampex EPS for 1/2″ pex)

idahobuild | Posted in General Questions on

Hey all,
I think that I an set on switching from 2″ XPS with 1/2″ pex over the wire mesh on the conc. slab to the Ampex EPS with pex channels.

With the 2″ XPS and wire mesh I was going to avoid having the pex under any partition walls.  With the Ampex I’m wondering if the pex being down in the channels is safe enough for a tubing layout that includes going under walls (more direct route) to get to rooms.

Does anyone have experience with the Ampex 2015F, or wall, hold-down anchor depths, that would have thoughts or suggestions as to whether I will still need to avoid going under walls?


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  1. Expert Member
    Akos | | #1

    Use anchors that don't go deep enough. With a 4" slab, you should have plenty of clearance. If you are worried, you can put one of those CSST nail plates over the pipes where the walls will go.

  2. Expert Member


    The anchors on non-loadbearing interior walls are in shear, so the minimum embedment is just 1". So if you decide to go down 1 1/2" , that means drilling a hole 1 3/4" deep. That should leave you with enough leeway to avoid hitting the pex runs.

  3. Expert Member
    DCcontrarian | | #3

    If you haven't poured the slab yet, and you know where the partitions are going to be, I'd put the anchors in the slab when it's poured. Drilling into a slab with piping in it makes me nervous as hell.

    1. Expert Member
      MALCOLM TAYLOR | | #4


      The concrete finisher I use is around six-four, two-fifty. My hope is to make it through my sixties without any more broken bones.

      1. Expert Member
        BILL WICHERS | | #5

        Malcolm, that is the best advice I've seen in a long time! :D


      2. Expert Member
        DCcontrarian | | #8

        Yeah, it was a dumb idea. I'm going to change my answer to mark the walls and take pictures.

        1. Expert Member
          MALCOLM TAYLOR | | #10


          Well I'm going to modify my answer to Idahobuilds to admit that while what I said was true, I'd be uncomfortable doing it. The consequences of puncturing a line are pretty big.

  4. Expert Member
    BILL WICHERS | | #6

    When you lay out your pipe runs, keep track of where they are so that you can mark them on the finished slab prior to drilling in anchors. This is easy to do: lay the pipe loops out perpindicular to the walls, then mark the walls where each pipe run is. Once the slab goes in, you can use a chalk line to mark the location of all the pipes by stretching the chalk line between the marks you made on the walls before the slab was poured. Now you KNOW where the pipes are, so you can just drill between them when setting anchors. Easy.

    I wouldn't trust most masonry anchors to reliably hold with only 1" embedment, I think you'd have some blowouts. My preference would be to go deeper, ideally closer to 2", but at least about 1.5". Use an SDS plus rotary hammer, which will make short work of the drilling, and use a depth stop to be SURE you don't go too deep (or just mark the pipe locations and don't worry about it). I prefer the expanding type non-lead anchors, usually sold as "Red Read" brand in the box stores. The kind I really like has three expansion leaves instead of the two the Red Heads use, but those come from one of my supply houses and I can't think of the brand name. Another option would be lag shields, but those are not nearly as reliable as the expansion anchors. Larger (5/16" or 3/8") tapcons are pretty reliable too, and are FAR less likely to give you problems than the 1/4" and smaller ones in terms of pulling out of the holes or breaking off when you're driving them in.


  5. jberks | | #7

    You will be fine if you stay on top of the crews. Explaining the depth issue.

    But, when in doubt, dymonic 100 at full coverage works. It's very solid with enough flex to manage contractions of dissimilar materials. It also doubles as a moisture barrier. However, I can't speak to the longevity. Maybe it'll delaminate in 50 years. Hopefully I'll be dead by then.


  6. idahobuild | | #9

    I going to go with a combination of the thoughts presented.

    1. Stay on top of the crews about the depth issues.
    2. Mark the piping locations on the stem walls/forms/etc. and transfer to slab
    3. CSST with some sort of galvanic protection from conc. moisture.
    4. Pictures and measuring
    5. when in doubt -- glue it :D

    sound about right?

    1. jberks | | #11


      Sounds like a good plan. Redundancy is important in critical systems.

      I had another thought that you might consider. And that's the radiant design and layout itself. For instance, I like to seperate each room into it's own loop, so you can independently dial in each room. So inherently it breaks up the tubing area and creates a "space" for the walls to go. I like to keep the feeds and returns in one area, like against a specific wall. So if you know where these are, keep good records, and stay on top of your crews and and the process you will be fine.

      When I say staying on top of the process, it means taking an integrated and systems design approach. As the lead, you need to know each independent system and how they integrate with each other as a whole, and communicate that integration to the crew on site that just showed up blind to your project that day. With words and with visuals (and a bit of emotion)

      So, before the rebar and tubing is going in, you mark out with marking paint on the sub-slab assembly where the base of the stairs and walls are going to go. So the tubers don't cross them. Don't forget to consider the finishes like vanities and cabinets, and if they're going to get screwed down.

      After the tubing goes in, take lots of pictures, with a measuring tape layed out, for reference. Ideally, you draw up an as-built in cad, so you can reference the dimensions later if you have to...

      Then, when the slab is poured, you once again mark the slab with painters tape exactly where the stairs, walls and cabinets are to go.

      Most crews hate this OCD stuff from a lead in any other circumstance, but I think EVERYONE gets it and gets on the same page when it comes to a radiant slab.

      Or just use dymonic 100...


      1. Expert Member
        MALCOLM TAYLOR | | #15


        That sounds like a good plan, but why mark off the walls once the slab is poured? Aren't the framers going to frame the walls from the drawings?

    2. Expert Member
      BILL WICHERS | | #12

      CSST is a type of flexible pipe used for natural gas. I'm hoping you're not planning to use this instead of PEX? PEX will certainly hold up better over time than CSST here.

      If it's just the nail plates, those are normally made for electrical applications, and can be found in box stores. They're made from a hard steel, I've always suspected cold rolled steel sheet, although I've never bothered to really check. You generally don't need to worry about corrosion of metal objects completely embedded within the concrete, since the alkaline nature of concrete acts to prevent corrosion of the steel.

      If you want to embed some protection into the slab above the piping in areas you plan to install anchors, I wouldn't use nail plates, since they're pretty small and concrete work is not known for high precision. Go to a metal supply house and get some pieces of ~0.1" thick cold rolled steel sheet, and have them cut those pieces into maybe 4-6 inch squares. Embed those in the concrete over the wall, or just get a long stip of the materail and place it in the general area of the wall. The larger size of the steel sheet will make it more likely to "line up" with whatever you're trying to line up with. If you're really worried about corrosion, use stainless steel sheet instead of cold rolled steel sheet, but keep in mind that corrosion protection is not really required here.


      1. Expert Member
        Akos | | #13

        I meant the nail plate for the CSST:

        These are made out of hardened steel and near impossible to drill through.

        1. idahobuild | | #14

          yea, I was thinking of the plates; not the pipe.

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