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radiant heating in concrete floor

Do-It-All Member Posts: 4

1) Do a heatloss calculation for your home. Most jurisdictions I deal with require one for the house as part of the building permit process.

2) All our basement slabs are insulated with 2" of Dow Styrofom SM (below grade variety) with R10 insuation value under the concrete slab. We prefer the blue Dow product because it is less fragile than the pink Owens Corning rigid foam variety. We seal all the seams between the insulation boards and between the boards and the footing with waterproof tape or membrane that has an adhesive which is not a foam solvent. We want to keep any groundwater away from the concrete layer (cold groundwater will suck heat out of the slab fast).

In building locations with high water tables we put lots of perforated foundation drain pipe in the 3/4" stone drainage layer under the insulation and run that to a sump.

3) You can install the Pex pipe several ways:
- to 6x6 wire reinforcing mesh, or
- to clips/tracks pinned to the sytrofoam

I prefer using tracks stapled to the foam, but I will use the mesh method for smaller areas. The tracks allow concrete to flow under the Pex, and leaves the pipe near the bottom of the slab where it provides the best thermal mass heating.

If you use the mesh method then be sure to lift the mesh to the depth required by the engineer for what the slab requires. But this will result in more erratic slab temperature swings because the Pex is higher up in the concrete.

Also consider installing a slab sensor in case you want electronic temperature feedback to the system controls. We typically use a Tekmar 0072 or 0073 sensor.

As mentioned, insulation at the edge of the slab is important. We typically build with insulated concrete forms in the basement, so the edge insulation is automatically provided.

See the attached picture of a portion of a 800 sq. ft. home theatre in a basement. This has 2" SM insulation with a full waterproofing membrane over the SM from wall-to-wall (the basement is below the level of a nearby lake). The red pipe clips can be seen on the membrane - these clips can hold 3/8", 1/2", or 5/8" pipe. Note the pipe sleeves at the transition from the slab to the manifold - we label them so we get the pipe to the correct position on the manifold. We also put the 6x6 wire mesh on top of the Pex pipe and lift the mesh to about 1.5" below the surface of a 4" slab


  • Michael G._2
    Michael G._2 Member Posts: 1

    I would like to install radiant floor heating in the basement of a new home. This would be installed in a new concrete slab. I had one person tell me to installate the floor with 1/2" extruded PS, install 1" chairs 2' apart, attach rebar perpendicular to the chairs, lay wire grid on top of rebar, and attach the 1/2" Pex to the wire grid. Since this is a basement would it be better to installate with 1-2" of extruded PS, lay my wire gride on top of installation and attach PEX to wire grid, and pour concrete directly on top.
  • Tom Kane
    Tom Kane Member Posts: 56
    radiant in slab

    Look at this site, you'll make your project a lot easier to install
  • Tom Kane
    Tom Kane Member Posts: 56
    radiant in slab

    www.crete-heat.com ......sorry for the double post
  • Brad White
    Brad White Member Posts: 2,398
    General Guidelines versus

    a real, calculated design, is the difference between success and failure.

    You have a great opportunity here, no question about it.

    Start with a heat loss, no matter what.

    Insulate with extruded polystyrene (EPS, the pink or blue board, not the white stuff). Use no less than R-5 underneath the slab and R-10 on the edges. Makes a nice compression joint too! That will better define and maintain your calculated output. Use a vapor barrier too.

    Spacing is a function of your heat loss and water temperature. As a general rule, the closer your spacing the more even will be the floor temperature and with concrete, that can be a very low water temperature indeed.

    This site and the Radiant Panel Association folks have good references to make your project a success. The details particular to your needs are too numerous to be covered here.

    Good Luck-
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • Scott OB
    Scott OB Member Posts: 22
    Crete Heat

    I just did a garage floor of about 900 square feet with "green" Crete Heat.R-10 with vapor barrier.Easy to install the tubing per engineered design.about 1 hour to lay all the tubing.Great product.
  • Don Regan
    Don Regan Member Posts: 43
    Thanks Scott...

    If you are the Scott from ME, I will be up there on Thursday in the Portland Area. love to say Hi.
  • Scott OB
    Scott OB Member Posts: 22

    It would be great to meet you but I'm in Puerta Vallarta until Saturday 10/20.I have some pictures I'll send you of the install when I return. Scott
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