On the insulation, in the insulation, under the insulation.

nibs

Running the DHW from kitchen to heater. 3/4" pex about 22 ft long. do I run the pex under the insulation, cut a channel in the insulation or lay it on top of the insulation. Concerns are heating the slab, interfering with the 1/2" pex radiant. Slab is 2" thick so there is not a lot of room, I have made a sheath for the pex to slow heat transfer, did not trust the hardware store foam insulation for water tightness. We plan on laying the Styrofoam tomorrow If I put it under the styro, it will be in styrofoam entrained cement so it will have some insulation. The cold line is in the sand under the vapor barrier.
Great site, learn so much just by reading the responses by the experts.
Thank you,
Tony

hot_rod

Almost needs to be under in a 2" pour, unless you determine a route within the radiant without crossing tube over tube.

Lay it within a radiant loop and just cut out some foam where you need to cross under the heating pex, maybe.

1/2 should be plenty for a kitchen? Unless it is 1/2 sleeved in 3/4?

Any fiber in your special mix to prevent "road mapping" or does it all get covered?

nibs

Bob, we do put fiber in the top slab, and make a strong mix.
The DHW line will not have to cross many radiant lines, but will be joining the pex for three home run loops, (6 lines) and will be joined in the next pour with another loop, so it is getting a little crowded in the hallway to the boiler room. If we put it under the 3" foam boards it will have about an r 2 insulation down to the planet and R 15 to the radiant. The sleeve cover on the DHW line is reinforced LPDE about twice the thickness of the pex.
Thank you.

hot_rod

Your concern is heat loss from the hot lines if under the insulation?

I know when plumbing lines are in radiant slabs the cold will always be slab temperature until you run it for a bit. Even under all the insulation it will pick up some heat.

Hopefully you don't have or expect water anywhere under the slab?

nibs

Thank you, I was wondering what the usual practice is, and I gather it is common to run domestic water lines in the slab.
We put the cold water line in the sand with the electrical conduits, mainly to get it out of the way, am leaning towards putting the DHW in the sub slab, but do not want to lose too much heat.

hot_rod

A jobsite I visited in Italy, housing complex on a solar/oil district system.
Everything goes in the upper slab, power, communication, H&C, gas, radiant. Masonry walls inside and out, foam filled blocks, stucco or plaster finish.

They use satellite boxes to join all the lines in the wall.