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Re: Radiant heat/conc. floor

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At 12:02 PM 8/27/99 -0700, you wrote:
>Does anyone have experience with a radiant heating system in concrete
>slab on grade? I have a client wishing to use this type of heating
>system. What precautions can be taken to ensure slab cracks not occuring
>at locations of pipes within the slab?
--------------------------------------------
In energy-minded Davis CA, radiant heating using flat coils of rather
pliable plastic pipe embedded in slabs on grade has been commonplace for at
least a dozen years. Davis has expansive clay soil that is notorious for
swelling up under the slabs and staying swollen. Soaking the clay a day or
two before slab placement is a locally enforced code supplement, but not
always successful. In my opinion, not all the intended pre-expansion of the
soil actually occurs before the slab cures, and the later stages of
expansion sabotage the slab. Enough time for the added water to get way down
is needed.

The radiant piping subcontractors expect to tie their coils to welded wire
mesh supported well above the bottom of pour. This mesh does not control
slab cracking very well.

Robust grids of rebar in the slab, over which is the mesh for the coils, is
the best palliative I know of for crack control. Yet I have seen cracked and
vertically offset slabs where the plastic piping did not rupture.

I have a brochure for copper pipe radiant heat from the early 1950's, but
that material seems to have given trouble and is long out of favor.

Davis Energy Group in Davis CA has lots of PE(ME)-level design expertise in
radiant heat construction. (phone is in Area Code 530.)

Charles O. Greenlaw SE    Sacramento CA