Pex - Is the extra cost worth it...

dko

Agree when fittings are used which there are a lot of in potable water systems or radiator pex piping. But in slab it should just be a continuous run with no fittings except at the manifold.

Solid_Fuel_Man

Long term quality of the oxygen barrier would be a consideration for me. 

I've used MrPex, Uponor, Vanguard, and Watts in a slab. I'd go with a USA or EU made pex-b for slab work. Like @GroundUp I don't see the benefit of pex-a where we are talking about long straight runs, and bending 180 degrees at the end. Those bends don't need to be perfectly tidy and fit in the 6" wire mesh grid. 

Personally I don't care about expandability on slab runs. It's going to be terminated with a manifold right? Compression connections generally.... so any pex will work. 

Most important part of a slab is protecting the protrusions where the tube emerges from the slab, and keeping sunlight off of it after the pour. Very few installs I see cover up the pex bundle with black plastic. I use black contractor's garbage bags and tape over the pex until the building is built. 

I really refuse to use China made pex.....

SIDE NOTE: every radiant slab I've done I connect all the loops together, plug the end and put at least 50 psi of air in the tube. That way if the concrete crew damages the tube somewhere you'll know it. I'm always on site during the pour, and have some couplings and shrink tube that will fit over my crimp rings and couplings. Wear tall boots in case you need to go in the crete! 

Robert_T

The little we pex have used has failed. We used white pex for hot water recirculation lines on a large apartment building and it developed pin hole leaks within five years. It was exposed on the basement ceiling so I"m sure glad it wasn't buried in the walls or ceilings.

ChrisJ

Robert_T said:

The little we pex have used has failed. We used white pex for hot water recirculation lines on a large apartment building and it developed pin hole leaks within five years. It was exposed on the basement ceiling so I"m sure glad it wasn't buried in the walls or ceilings.

How long was this pex exposed to sunlight before installation? Was it exposed to sunlight via basement windows?

What brand pex was it and what temperature was it running at? City water?

LMacNevin

I've been involved with PEX manufacturing, standards, and testing for a long time, and here's my unbiased advice: If the PEX tubing is third-party certified to industry standards ASTM F876, ASTM F3253, or CSA B137.5, then it's a reliable product that will meet or exceed requirements.
Tubing with a higher degree of crosslinking will typically have slightly better flexibility. I won't get into the explanation of that here.

PPI has a document called TN-17 that explains many details about PEX https://plasticpipe.org/common/Uploaded files/Technical/TN-17.pdf

PPI also has a webpage all about PEX https://plasticpipe.org/BuildingConstruction/BuildingConstruction/PEX.aspx and a webpage all about PE-RT https://plasticpipe.org/BuildingConstruction/BuildingConstruction/PE-RT.aspx.

We encourage users to purchase products from PPI member firms, which are shown on those webpages.

GGross

Robert_T said:

The little we pex have used has failed. We used white pex for hot water recirculation lines on a large apartment building and it developed pin hole leaks within five years. It was exposed on the basement ceiling so I"m sure glad it wasn't buried in the walls or ceilings.

I hope you went after the manufacturer and either got warranty or figured out what was done wrong. We have been in wholesale distribution of pex tubing for over 25 years and have had exactly 2 failures, these are single point failures as well. One the installer expanded fittings too close together, cracking a coupling, and the other burst because they were using it on near boiler piping for a wood boiler that ran wild and exceeded max temp of the tubing.

dko

Pretty much every manufacturer mentioned in this post from cheapest to most expensive is on the PPI list.

hot_rod

Pex used in plumbing sees more severe conditions like pressure and continuous water water treatment chemicals added. Possibly higher water temperatures. Constant domestic water recirculation can also have an effect on some pex types.

Search around there have been a number of pex failures on DHW recirc applications, lawsuits still lingering.

Good idea to jacket the heat pex tube if is exposed to UV. A few pex manufacturers offer a protective jacket you can slide over the exposed tube. UV can be an issue even inside a building. Tube stored outside in the sunlight can break down the O2 barrier quickly.

There is a row about 12" long on pex tube with various listings, so all pex is not created or tested and passed to the same degree.