5/8 pex, or 1” Aqua pex, or repipe?

Mosherd1

Customer had house built 10 years ago and is ready to have the radiant hooked up feeding the garage floor. The garage is 28 x 28, 10’ ceiling, (2) 9x8 insulated garage doors, one steel man door, and one 3x4 double pane window, 2x6 construction with 2” closed cell spray foam, r 40 cellulose in the attics. There are 3 loops of 1/2” oxygen barrier pex. This past summer, customer had the basement finished, and the contractor ran 1” AQUA PEX from the garage manifold location, to the mechanical room through the basement ceiling. I told the customer about the importance of having an oxygen barrier, and he completely understood. I believe we could push 5/8” oxygen barrier pex through the 1”.  Doing some rough math the heat loss in the garage should be around 15,000-16,000 btus. Figuring each loop in radiant floors should flow ~1/2 gpm, and there’s 3 loops that’s only 1.5 gpm, so in theory, I could be able to use 1/2” pex for the feeder, correct? So 5/8” should work while lowering the head pressure, correct? Or should we use the 1” Aqua pex? It is a closed system and all the other tubing in the house is oxygen barrier. Or do some damage to the new ceiling and run 3/4” oxygen barrier pex? There is approximately 40’ of pipe between the garage manifold and the mechanical room.

mattmia2

If your heat loss is correct it should work. I'd have 3 concerns. What will your recovery time be from opening the door? Is the run straight enough that you can push another tube through it? Will it be protected from freezing?

Another option is to connect it with a hx and run glycol and nonferrous components through the aquapex and in the garage. The hx is another option even without glycol.

Big Ed_4

My thoughts , if the 1" is not heat Pex , what about the 1/2" in the floor ? Stainless heat exchanger to separate the heating systems would be my recommendation .....

hot_rod

the pex in pex should work and be the least expensive fix
with a hx you need another pump, expansion tank, purger, fill system

Mosherd1

@Big Ed_4the tubing poured in the concrete is 1/2” oxygen barrier pex, it was done 10 years ago when the house was built.  The contractor who finished the basement this summer ran the non oxygen barrier pex. 

GroundUp

Unpopular opinion, but I have opened up dozens of non-barrier pex radiant systems and have never once seen any evidence of oxygen intrusion. High temp is one thing, but a radiant slab with a heat loss that low should never need to exceed about 80 degrees with the supply water. While using a barrier tube is the correct route, we'll both be dead before the AquaPex causes any trouble in this scenario. You should easily be able to feed those 3 loops with 5/8" tube if you're able to fish it through there though, so I guess I'd try that method first and if it fails, just use the AquaPex.