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Radiant heat

Hello. Thanks for the add. I have a client who wants concrete slab with radiant heat. He also wants real nail down hardwood flooring.

What makes more economical sense?

Slab with attached warmboard then nail down hardwood.

Slab with engineered hardwood

Wood floor system with radiant either in warmboard or between joist

TIA

Comments

  • nibsnibs Posts: 376Member
    Here is an idea that many will criticize as being unfounded or to far off the wall.
    Lets assume a 5" slab, every 16 or 24 inches cast a 2X4 on the flat directly into the slab flush with it's surface, you can put screws into the edges not driven all the way in, 'round here they call it porcupining the wood, to bind the wood firmly into the cement. Now you have nailers for the flooring. Wood cast into wet cement will not rot as the cement is absorbed into the wood surface and protects it from rot. Over the years I have done this several times, to give me embedded plates for fastening walls etc, years later the wood is still sound. Makes screeding & finishing the cement a breeze.
  • ZmanZman Posts: 5,334Member
    If it is true concrete slab, trying to float in wood sleepers would be a PTA if not impossible.

    If the floor is wood framed, why would you pour concrete if what you really want is wood? Low mass systems with transfer plates installed on the bottom side will provide a nice fast reacting system without the thermal flywheel effect you get with high mass.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • hot_rodhot_rod Posts: 12,037Member
    I did a few jobs where two layers of 3/4 play were glued and nailed to the slab, hardwood nailed over that. It give you better thermal conductivity compared to 2X4 sleepers nailed over slab.

    I have not found a real eloquent way to put nail down hardwood over a slab. An engineered hardwood would be ideal for wood over concrete.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • nibsnibs Posts: 376Member
    @Zman embedding 2x4 on the flat is easy you just fix it to the rebar and adjust the el to suit. Makes the finishing & placement a breeze.
    The OP says owner wants a slab.
  • hot_rodhot_rod Posts: 12,037Member
    Ideally you want to use pressure treated wood when it is in contact with concrete. My experience is that any dimensional PT wood shrinks and twists as it drys, so that needs to be managed somehow.
    If you glue and screw them to concrete you can keep them fairly straight, they will still shrink a bit.

    I can't imagine concrete installers/ finishers would working around suspended 2x4's so easily. Possibly for a very small DIYer project?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • Steve MinnichSteve Minnich Posts: 2,474Member
    I’ve done 1.5” gypcrete with sleepers/nailers and hardwood, but never what’s being suggested here.

    I remember the double sheets of plywood method from a very old Fine Homebuilding article; still have it.
    PHC News Columnist
    Minnich Hydronic Consulting & Design
  • ScottSecorScottSecor Posts: 329Member
    I too would be concerned about wood sleepers. My suggestion (assuming it's a slab on grade) is to embed the tubing and instead of wood flooring suggest porcelain tile that looks like wood. Very stable, looks fantastic with the wide plank style.

    If client insists on hardwood, I'd suggest something like Warmboard over joists.

    Not sure your building a slab, or over a crawl space or basement.
  • hot_rodhot_rod Posts: 12,037Member
    here is an example of a few National Wood Flooring Association hardwood over radiant slab, from the RPA Flooring Guide
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • ZmanZman Posts: 5,334Member
    nibs said:

    @Zman embedding 2x4 on the flat is easy you just fix it to the rebar and adjust the el to suit. Makes the finishing & placement a breeze.
    The OP says owner wants a slab.

    @nibs
    If I remember correctly, you did your floor by hand mixing in small batches. That works fine for a HO who has time to spare.

    No professional concrete crew, anywhere would do it that way.

    Sometimes it is the job of the pro to educate the homeowner and help them make a good decision. "The customer is always right, unless they are wrong in which case it is your job to tell them so...."
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • nibsnibs Posts: 376Member
    @Zman
    At the outset I said that my suggestion to too far off the wall, for many.
    You are correct about how I did the floor in my build, I did two areas where I floated a 2x4 into the mud. Have done several over the years, with screw heads sticking into the mud by an inch or two (porcupine).
    I will say that the lumber does not twist or bow, untreated wood cast into wet cement will not rot (old timers used to know this).
    Biggest problem is with acceptance either by crews, owners, or inspectors.
    Ask that if you come across a situation where you think it may be effective, use it, otherwise discard the idea and move on.
    Cheers.


  • edited June 4
    Edit: Lost connection to brain.
    Often wrong, never in doubt.

    Click here to learn more about this contractor.
  • ZmanZman Posts: 5,334Member
    @danrobbins_19
    You have left us talking to ourselves..
    Are you out there?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
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