Pond Boss Forums GENERAL QUESTIONS Help Pex radiant heat installation

We are just about to pour a slab in our garage/apt that will receive Pex radiant tubing. The slab is 15' x 27' planned at 5" thick.
I have a roll of 1/2" x 1000 ft O-2 pex, a set of 3 circuit manifolds, and the staples for the 2" high density foamboard. Nick and Jersey have been very helpful and inspirational with their radiant heat projects.
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I plan to put in a perimeter of 1.5" hi density foam to isolate the slab from the exterior walls. The slab support is pea gravel/6 mil vapor barrier/2" hi-density foamboard. The reinforcing is #4 rebar; I have enough to put it at 12" o/c and suspend it on 2" bar support chairs.
WRT the Pex...
Although it is not my goal, if I get into a situation where one run must run over the top of another line, is this a huge NO-NO? Being midwestern, I plan on about 10" spacing at the slab interior and 5" - 6" at the three exterior runs.
What's wrong with this picture? What am I missing or not thinking of?

If memory serves the maximum length for one loop of 1/2" is 300 feet, (4) loops of 250 feet would be better. If you can layout your run lengths to be within 10% of each other you can eliminate the need for flow balancing. I took some extra time to layout my runs on CAD to optimize/equalize my loop lengths. I also layed it out so the hottest water ran through the perimeter tubing.

I'm not a radiant expert (although I did pretend to be one last year when I built my house) but I doubt if one crossover would hurt. It's not a "best practice".

Thanks jsec.
By nominal calc's, I will be using about 600 feet total. I do want to run 3 separate circuits.

Not sure I understand how this would relate to a simple 3 circuit system that comes off of one manifold. ??

The Pex out from the hot manifold should run closest to the outer perimeter, rather than the portion of the pex loop that is closest to the return port of the manifold. The tubing should be on the very bottom of the slab, and stapled to the insulation. Visqueen between the gravel and the insulation? You're spot on in placing the rebar on chairs in the center of the slab. 2' OC for the #4's will allow the guys spreading/screeding the concrete to step around the rebar and avoid stepping on it, bending it or smashing it into the Pex.

After the Pex is installed, pressurize the system and leave it hold pressure for as long as possible to ensure that you don't have any pinhole leaks.

Not that you don't, but take very good pics (even with some sort of measuring stick in the photo) to allow you to find those runs under the concrete just in case you ever need to drill into the floor. I was told that if I ran Pex outside for snow melt, it should be 3/4" and 6" OC.

OK...now I get it; thx

Also if you plan to have a bathroom stay away from the stool area or I have heard you can melt the wax ring and the stool can leak. Just a thought.

dap, great tip!!!

OK, so here's a question. Suppose I get the pour prepared, all the tubing stapled to the foamboard and the circuits securely attached to the manifold and I pressurize the system. The pressure very slowly drops. I suppose the correct fitting check is with soapy water. I find nothing leaking. This leaves the tubing circuits. How do you find a leak there? (before it's buried in wet, bubbly concrete)

You can isolate the circuits one at a time to find the leaker, no? After that, I think you get to check a couple hundred feet of line for bubbles.

Bubbles? The lines are filled with air during installation.

Air (pressurized) on inside, soapy water on the outside (use a bucket and a paint brush), bubbles at the leak. As much fun as finding a gas leak, without the possible pyrotechnics.

This was the method I was hoping to avoid. Somehow, I hoped for a simpler procedure.

Chances are 99% that any leaks will be in the fitting attachments, rather than in the tubing. Those won't take too long to paint with dishwater.

I doubt you get any leaks in the tubing itself unless it has been roughed up against the rebar or something else nasty. OTOH, I once spent an entire day troubleshooting all MY connections in a pair of electrical circuits before finding one length of 12-3 with ground that just had an internal flaw apparently dating from manufacture.

Brettski:

You have shutoffs at the manifold on each run, correct?

si

Bueno. Es más fácil para encontrar las fugas de esa manera, y si se desarrolla una fuga en el camino se puede eliminar que se ejecutan desde el sistema.

Sunil...if you please?

"Good. It is easier to find the leak that way, and if a leak develops in the way you can eliminate that run from the system."

P.S. I translated the "good" part all by myself!

Not bad Theo! Brettski is lagging behind I see. I don't know where I learned more, 2 years in High School, working on the South Side of Chicago or living in So. Cal.

I was better years ago, and it made travelling in Mexico easier, but now if someone starts talking quick in Spanish I'm lost.

...you underestimate

Es la peor parte de la ciudad.

It all depends, I do like fishing out of 95th street for spring coho. Very good eating. Never had a problem but still take personal protection

Theo:

Depending on where you go it gets much worse!

I suppose things could have changed since Croce's time.

They have believe me! Mom & Dad's garage has been "tagged" 3x in the past 4 years.