[Greenbuilding] PEX location in concrete slab

[answers at healthyheating.com]

Here's a FEA image for radiant tubes in a 4" slab located on the
insulation. Notice the quality of the surface temperature. 

http://www.healthyheating.com/Page%2055/Images/Drawing2.jpg

 

Using ones imagination you could see how raising the tubes upwards
reduce the surface temperature quality by creating high and low
temperature points on the surface.  To correct this one would have to
use variety of simple techniques including using a higher density of
tubes operating at lower temperature.  

 

I've also pulled some selected text from ACI 318-02 Building Code
Requirements for Structural Concrete, on embedded pipes (There is a
newer version, when I get back to the office, will check to see if this
section has been revised).

 

CHAPTER 6 - FORMWORK, EMBEDDED PIPES, AND CONSTRUCTION JOINTS

6.3 - Conduits and pipes embedded in concrete


6.3.5.1 - They shall not be larger in outside dimension than 1/3 the
overall thickness of slab, wall, or beam in which they are embedded.

6.3.5.2 - They shall not be spaced closer than 3 diameters or widths on
center.

6.3.6.3 - They have a nominal inside diameter not over 2 in. and are
spaced not less than 3 diameters on centers.

6.3.8 - No liquid, gas, or vapor, except water not exceeding 90 F nor 50
psi pressure, shall be placed in the pipes until the concrete has
attained its design strength.

6.3.9 - In solid slabs, piping, unless it is for radiant heating or snow
melting, shall be placed between top and bottom reinforcement.

6.3.10 - Concrete cover for pipes, conduits, and fittings shall not be
less than 1-1/2 in. for concrete exposed to earth or weather, nor less
than 3/4 in. for concrete not exposed to weather or in contact with
ground.