Hydronic floor heating: Onix vs Pex, other recommendations

[stevenl]

We have to replace 2 floors of Entran 2 staple-up, 1,00 sqft each, in our office bldg. To make this easier we will switch the upper level to hot water baseboard, and the lower will again be radiant hose attached to the floor ply. Thankfully its a generous 5-6' crawl space.

But my choice of Onix vs Pex in the staple up is provng difficult. My online research, and indeed the heating contractors bidding, reveal serious skepticism with Onix (discoveries of "black gunk", or "ferrous oxides" clogging these systems), while others have complete faith in Onix over Pex.

I understand the Tdelta expansion issues of Pex. Onix would be my choice, except for my current experience of a rubber hose that lasted only 17 years. Advice would be appreciated!
-stevenl

 

[Drazen]

The fact with design work is that we mostly rely on papers, certificates, and experience comes with time and feedback only.

As much as I know, that is new material, so there is no long-years service.

What you can do is to check whether manufacturer can provide some quality institute certificate, ageing test in particular.

The other thing is duration of after-install warranty.

There could also be fine print of installation conditions, issues of design - comparative roughness vs. similar pex diameters.

I don't know how it works in your area, in mine bidders would not be responsible for majority of issues mentioned, they just install and go, they even have no any legal responsibility to provide you with equivalent capacity, but with "good guess" only.

Even if you decide on Pex, you can have trouble with "almost the same" installation.

Plainly, if you do not want to burn your funds, mechanical engineering consultant is very recommendable.

 

[stevenl]

Thanks,
Good advice.
PEX is code approved and has a longer track record. Onix is not specifically code approved from what I can see, though the ICC report on Onix looked o.k.. I will ICC call about possible updates.

I did speak with a mechanical engineer. He was not aware of issues with either product.

 

[Drazen]

Out of curiosity I have read one brochure about Onix where it is stated that "better heat transfer coefficient enables dry installation without aluminum "equalizing" plate.

Though man should be specialist in thermodynamic modeling to give 100% competent judgment, this is highly doubtful for me as aluminum plates are mostly used to improve problems with installation geometry and they help whatever material is used to enable lower tmax vs. tmin difference, which is affected by pipe spacing, pipe diameter, height position of the pipe, all geometrical parameters, not related to material in any way.

And such unclear but bold statements increase my vigilance, as a rule, at least until they are not proprely backed with arguments.