DIY Hydronic Floor Heating

[AC_Hacker]

Originally Posted by pachai

I discussed insulating the slab with my builder, and he reported that he has another project where he is repairing a slab that collapsed on the styrofoam. So, right or wrong, I am going to let him pour a normal (up to code) slab.

It certainly is difficult to try to push for energy saving options once the construction process is underway.

The contractor's role is to get the job done and move on to the next job.

Your contractor may have had a failed insulated slab, but that does not mean that all insulated slabs fail. Insulated slabs are done routinely and successfully all over the world. It's a matter of proper design & construction technique.

As the above illustration of heat-loss gradient shows

• heat loss is greatest through underground walls and foundations,
• next greatest at the edges of uninsulated slab floors,
• next greatest at the perimeter of an uninsulated floor
• least at the central part of an uninsulated slab floor

So the pay-back will be most favorable in the highest loss areas. However, when a radiant floor heating is contemplated, the floor becomes the heat source and it is in contact with the world's biggest heat sink. So slab insulation is of the greatest importance if the radiant floor is to be efficient.

Foundation Insulation

Slab Insulation

From the second link:

Determining How Much Insulation

The RPA Guidelines provide a simple formula for calculating the R-value for heated slab insulation. Subtract the inside design temperature from the outside design temperature and multiply by 0.125. For example a 70° F inside temperature minus a 0° F outside design temperature multiplied by 0.125 equals R-8.75, approximately 2" of polystyrene board insulation. This insulation should at least be installed around the perimeter of the slab to below the frost line. (If this is not possible, it can be installed horizontally four feet under the slab.)

There are many good books that address the daunting task of building an energy efficient house in the country that is the [second] biggest energy consumer in the world (the book images are hyperlinked):

-AC_Hacker

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