Suggested pex for sandwich style system?

Midnightsnacker41

I'm putting radiant heat in my basement. I have 2 inchs of rigid foam insulation, with a layer of OSB on top. I'm then going to put a second layer of 3/4 inch OSB on top, but cut into strips so there is a 3/4 inch gap between the strips. I'll run 1/2 inch pex (with aluminum heat transfer plates) inside the gaps between the osb. The final flooring will be Lvp installed on top it the subfloor.

What type of pex should I use? If it expands, will it lift the Lvp up?

Jamie Hall

The PEX must be the oxygen barrier type — there are several good brands. Otherwise, if you're wondering about PEX A, B, or C — that's a matter of flexibility and joining methods.

On expansion, yes indeed the PEX will expand. Any kind. But it is not a problem of expanding to lift what is on top of it; it won't. What it will do is get longer as it gets warmer, so what you must do is provide space at the end of each run for it to expand freely.

hot_rod

If you use a good brand extruded type transfer plate, the tube will be held tightly in place. Allow room at the end 180 turns for expansion, don't clip the very center of the 180 return loop.

The thinner flashing aluminum type plates don't generally pinch the tubes tight enough, and the tube will expand and push up..

We used a pneumatic palm nailer with a rubber tip to push pex into the extruded plates, much easier than a rubber mallet when you are doing thousands of feet of installation.

Installers find the A type pex to be the most flexible to work with.

Reset controls or constant circulation, help limit wide fluid temperature swings which limits the tube expansion.

The tighter the tube spacing the lower the SWT, faster the response, and kinder to the final floor covering. I like 6" on center for those reasons.