Oxygen ingress, fact or fiction?

That's some aggressive water! Was it ever tested/ treated?

I'm no scientist, but I think its very clear that is the case. Mad

I know Tom...definitely enigmatic but so are alot of things in heating that leave us scratching our heads. The oxygen permeation through the "naked" tubing seems like the same principle as "high pressure goes to low pressure....and Hot goes to cold."

DIN Standard 4726 addresses this. I would have to do some digging to find some of the Wirsbo videos that we made of the testing process and the results but it is amazing how fast issues occur. Nature hates an inbalance.

Comparing rubber tube to non-barrier pex is no different than comparing a dirt floor to a reinforced concrete slab. They both do the same job, but with extremely differing effects. I cut into maybe 10-15 non-barrier pex systems annually, some fairly new and some older than me. Not once have I seen any evidence of troublesome o2 ingress where there wasn't also oxygenated site makeup water being added. While I would never install non-barrier tube in a hydronic system for any reason, it's not nearly as detrimental as some very influential forms make it out to be. I've been asking for upwards of 10 years for anybody to show me some evidence of problematic o2 ingress in a leak-free NB pex system, and have gotten only crickets. Maybe this post will change that for me?

Because it doesn't have an oxygen barrier and I do things properly when the opportunity is given. Any ingress is worse than none, right? This whole "I know everything because I read it in a book" attitude is getting pretty tired. Almost as tired as the passive-aggressive shots at anybody who challenges these "facts" that nobody has previously had the experience and willingness to challenge. This trade came to be what it is today by trial and error along with people willing to put in the time and effort to write the book. The book was written with what was known at the time of writing- adaptations are necessary sometimes as things are always evolving. Smugly responding to new data with "nuh-uh", is no different than arguing with fuel injection when it came out. Once we stop willing to learn and adapt, we fall as a trade and as a people. Learning is good for everybody.

Basically this discussion goes back to 1974.
And it was not just trial and error on the field

This was a good read for me
Article: The Oxygen Diffusion Debate - Defused

Notably: "The general rule is: if the total amount of steel
surfaces are 5 times larger than the plastic pipe surfaces,
tubing without barrier can be utilized."

There's a lot that leads up to that and more afterwards so wouldn't take that at face value. Just mentioning it as it's possible a system with a huge combined steel surface area + non barrier may not see the quick failures of expansion tanks as others where it is the only ferrous equipment.

The most widely used oxygen barrier is EVOH on the exterior of pex. But that only minimizes the ingress of O2, not completely block it. So the amount of tubing, temperature, and environment affects all results.

I mention environment because pex is not the first/main use of EVOH (food plastic industry). EVOH has great oxygen barrier properties but it loses a lot of it's barrier properties in high humidity. This is important and a reason why many manufacturers opt for moisture resistant protective layer on top of EVOH calling it 4 or 5 layer pex depending on if they count the adhesive layer.

There is a major manufacturer of EVOH barrier pex that makes it without this protective layer. And is one that relabels for many other brands. Rifeng. Supplyhouse (bluefin), Pexuniverse (everhot), Riifo, Zurn, Watts, and more. Not that big of a deal in most cases, but something to note if the outer layer of pex will ever be in contact with moisture. And to be careful dragging pex on the ground.

They do make pex-al-pex and evoh pex with a protective layer, but if you were comparing pex tubing pricing online and they are both pex-b or pex-a oxygen barrier, there are such differences that are not explicitly stated.

It was picked out as a reasonable explanation as to why some of the systems GroundUp has encountered with non-barrier pex did not have these specific failures as of yet. Not that you should be installing non-barrier pex because it's potentially ok.

I wonder if water quality (low ph) with higher temps accelerates the destruction that we are seeing.

How ironic that you mention acting like everyone should believe you just because you said so. Isn't that exactly what Hot Rod does with almost everything questionable? I have been asking for proof of non-barrier pex causing corrosion issues for over a decade and have yet to receive any. I asked again here and got nothing. On the contrary, I provided photographic evidence of one particular NB system with no corrosion after 24 years. Now it's somebody else's turn to provide some evidence to their claim. This is kind of like the dielectric fittings at dissimilar metals transitions. Everybody says you need them, but nobody can provide an exmaple of electrolysis or galvanic corrosion on one such joint in a leak-free closed loop hydronic system. This corrosion also comes from oxygen ingress, which is not present in such a system. All I want to see is proof of detrimental o2 ingress through the pex tubing itself.