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backer board over radiant floor boards

WillyP
WillyP Member Posts: 44
I have heard conflicting answers about using concert backer board over warmboard or in my case Sunboard (thank you for recommending them). My plan is to install the pex tubing boards, cover them with backer board, then tile over the top. Is this a terrible idea? Has anybody done that successfully? With my skill set, this would be the easiest way to do it.

Comments

  • hot_rod
    hot_rod Member Posts: 14,785
    From a temperature standpoint. If so the manufacturer should have a temperature number in mind.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • WillyP
    WillyP Member Posts: 44
    From what I can see, it is safe up 200° F. I am more concerned with the thermal mass.
  • ethicalpaul
    ethicalpaul Member Posts: 2,986
    edited December 2020
    I did Uponor Quik Trak in my bathroom...IIRC Uponor recommended setting a concrete board layer on top of the track board. Out of curiosity, what other way would you do it? And what is the thermal mass concern?

    Yeah, here's the manual: https://www.pscia.com/ASSETS/DOCUMENTS/ITEMS/EN/uponor-a5060761-install-instructions.pdf

    1 pipe Peerless 63-03L in Cedar Grove, NJ, coal > oil > NG
  • TAG
    TAG Member Posts: 487
    Take a look at the Warmboard instructions -- they have 6 ways to tile over. My installer is old school -- did more of full wet bed for the bath floors. Same for the one large shower floor. In the other bath I wanted to do the walls with some tube as part of the shower touches an exterior stone wall -- we just went over the Warmboard treating it as if the grooves were not there
    WillyP
  • Rich_49
    Rich_49 Member Posts: 2,565
    Use Hardi backer of the 1/4" thickness . This is what SunBoard recommended for their SunFoam product before Graphite pricing went crazy . The R value of the added backer is not an issue
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    732-751-1560
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
    ethicalpaul
  • hot_rod
    hot_rod Member Posts: 14,785
    CBS "cementitious backer systems" are needed you you are installing ceramic tile., if you follow the tile council recommendations. For wood or linoleum it is mainly an good backer system.1/4 plywood would also work for a backer for glue down or floating floor, might be easier to work with.
    The cement board does add a small amount of thermal mass, and would spread the heat laterally from the tube area also.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    ethicalpaul
  • WillyP
    WillyP Member Posts: 44
    I am using ceramic tile. That is why I plan on putting down backer board.
    ethicalpaul
  • WillyP
    WillyP Member Posts: 44
    To answer ethical Paul I read in another forum that the backer board doesn't work well because it has too much air space in it. But I now realize whoever wrote that, didn't know what they were talking about. At least that is what every expert I have spoken to has said.
    With pex in concrete (which I will do on the first floor) the concrete heats up and holds heat due to its mass. I was afraid that backer board wouldn't do that.
    ethicalpaul
  • hot_rod
    hot_rod Member Posts: 14,785
    There are some foam core backer board, a poly-iso core, I would not use that type.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • WillyP
    WillyP Member Posts: 44
    Mr Rohr while I have your attention. By any chance, do you know the normal exit temperature of water, when it leaves a slab in a pex in concrete slab application. It will be entering at apx ninety five degrees.
  • hot_rod
    hot_rod Member Posts: 14,785
    The temperature will vary as the slab starts and as it warms. You may see a wide ∆ on cold start, it closes as the slab warms. There really is no one exact number. If you designed for a 10° delta you may occasionally see that.

    If it enters at 95, exits 85 the AWT= 90.
    Surface temperature of say 82 in a 68° room would be about 28 btu/ hr delivered to the space.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    WillyP
  • PC7060
    PC7060 Member Posts: 317
    Concrete backer board must be set over a bed of thin set and mechanically anchored per the schedule. Just be careful where you set the edges and screws since you have radiant piping. 
  • Paul Pollets
    Paul Pollets Member Posts: 3,393
    I make an outline of the tubing layout using a sheet of clear plastic and a Sharpie, cutting the plastic sheet to the exact size of the room. After the tubing is traced the backer board can be set and the plastic sheet layed over the top to see where the tubing is. This allows easy screwing of the backer board without fear of hitting the tubing.
    PC7060WillyP
  • HomerJSmith
    HomerJSmith Member Posts: 1,292
    The governing factor, I would think, is the R rating of the substrate. The lower the R factor the better it is.
  • WillyP
    WillyP Member Posts: 44
    Paul. I plan to just use a sharpie to mark the studs on the outside wall. Then as I lay each piece I mark the pipe on top of the sheet.
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