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Hydronic pex tubing under tile

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I have a home with an unusual construction that does not allow me to put pex under the wood floor. The rest of the home has the floor raised a little over an inch above a Hardwood floor and the room in question will be tile. I know the structure will withstand the weight of the tile since the adjacent bathroom has had no problem. In the Bathroom, I used an electric floor heat product that works nicely. Partly for utility cost, I would rather use the Hydronic system to heat this room from the floor. I can't use any of the commercial products because I lack the room and that also prevents use of an embeded tubing. I plan on using 1/2 (actually .42) Hardi backer over a thin-set with slots cut for the 3/8 pex tubing. I have some questions. The tiles are about 6x12 inches and in a running bond pattern, would it b better to go lengthwise or crosswise to the pattern? Also, since pex expands when heated would it be best to allow for that expansion (I have figured out a way to do so, but most commercial products do not have any allowance for the expansion.

I will be monitoring both the floor heat and the room heat with a thermostat, should I also monitor the maximum return temperature of the water and keep the pex at a moderate temperature? I know of no commercial product that will do that but I have figured out a simple way to do so if needed. Currently the system is operating up to 180 on the loops.

Comments

  • Gordy
    Gordy Member Posts: 9,546
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    Yes allow for expansion of the pex at the turns, and run tile perpendicular to the pex runs.

    Make sure you use O2 barrier pex

    You will need a mixing valve to run lower water temps for the pex loops in that area. 180 is much to hot.
  • WGW_House
    WGW_House Member Posts: 3
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    Gordy, Thank you for your comments, I pretty much figured that. I do happen to have a new mixing valve I could use but there is no cold water source to use with it, my system is closed, with an antifreeze mix in case the heat fails and the crawl space goes too low. We travel a lot and have lost gas pressure a few times. we have electric backup in the house proper to prevent potable water from freezing,. my solution was to turn the feed for the floor off and on while monitoring the temperature. The feed for the floor is off the main line using diverter Tee's. I can easily monitor the input and output temperatures and programming a small processor to operate a valve to do this. What do you think the max temperature should be?

    The other thing is that the temperature may actually be much lower than than the loop set point. I just was able to hold my hand on the small radiator in a floor register that was ahead of that in the loop, and I know I can't withstand 180F. I will measure the temperature there.
  • Zman
    Zman Member Posts: 7,605
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    You don't need to mix in cold water from another source. The mixing valve circulates water through the radiant loop and blends in boiler water as needed. Be sure to use a valve which is designed for radiant as other models may have resistance that is too high for little radiant circulators . Check out the taco I series valves. They have outdoor reset and boiler condensate protection built in.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    Gordy
  • Leon82
    Leon82 Member Posts: 684
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    I don't think the tile will last long with that type of installation. Large format tiles need a sturdy floor and there are gudelines for floor deflection. It may be ok but I would research it a little more.
  • Gordy
    Gordy Member Posts: 9,546
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    A deflector calculation would be the proper way.
    The John bridge tile forum is a great place. About like heating help only it's about tile.

    The most important thing is the span the floor joists cover, and the sub floor. The hardi backer adds zero strength especially when you are using it as a sleeper material for radiant.
  • WGW_House
    WGW_House Member Posts: 3
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    Leon82,
    Thank you for your comment.

    I have used this same tile over much less sturdy floors in the past without problems, one of those was in the same home with electric floor heat. I don't really think of 6x12 as large format, at least in the areas I have lived. They usually only refer 12x12 and larger as large format. This installation differs only from the last in that I will be using hydronic heating through 3/8 pex tubing. None of my installations have had any cracking or grout loss, the oldest being now 20+ years. On the oldest I used only 1/4 board, and the floor had much more deflexion than this one does. I am not worried about that, I am most concerned with the issue of the pex under the tile and want to be sure it does not cause issues.
  • Paul Pollets
    Paul Pollets Member Posts: 3,658
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    I'd be stapling the tubing to the subfloor on 6" centers, embedding in a min of 11/4" lightweight and then applying a fracture-proof membrane over the thin slab before tiling.
    GordySTEVEusaPA
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
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    WGW_House said:

    ...I know the structure will withstand the weight of the tile since the adjacent bathroom has had no problem...

    Yeah, now you're at least doubling the weight. Tile is heavy, and only the slightest deflection, especially with bigger tiles, will cause a crack.

    I like @Paul Pollets_3 idea of the membrane, although I'd rather do wetbed than gyp-crete. But it adds a lot of weight.

    There was an error rendering this rich post.

  • Paul Pollets
    Paul Pollets Member Posts: 3,658
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    Usually one small area is way to small for gyp. Dry pak morter bed is the best way. Or Climate panels with Hardy board on top. Fracture proof membrane over cement or Gyp is always highly recommended