This question was sent as a response to my post "Acid Water and PEX Tubing":
What about the buildup in an in-floor heating closed loop system? The contractor used black iron fittings to connect manifolds to loop piping. There is a significant amount of rust and there is no filter or inhibitor in the system. What, if any inhibitors do you recommend? on Acid Water and PEX Tubing
For in floor closed loop systems where the water will contact any ferrous material (i.e. boilers and black pipe fittings), the PEX tubing to be used needs to have an oxygen barrier. Regular PEX tubing for potable water does not need nor have an oxygen barrier. The oxygen barrier prevents air from permeating the tubing (which it can do) because air will cause the iron and steel components to deteriorate into rust.
There are a few ways that PEX producers create an oxygen barrier. Two that I know of include what is called PEX-AL-PEX tubing which is a layer of aluminum sandwiched by two layers of PEX. The other type is Wirbo brand HePEX which has a compound that coats the inside to prevent oxygen diffusion.
If your plumber used HePEX, then you can somewhat see through it. Whenever fresh water is started off in a closed loop system, it is still full of enough oxygen to cause some corrosion for about 72 hours, before what some of us in the water industry say the water becomes dead. The HePEX will change from clear to a dark orange or even black. That is possibly what you are seeing.
Whatever type of PEX your plumber used, it will be labeled, and you can check the labeled name on the internet to ensure that it is actually an oxygen barrier type tubing. If it is not oxygen barrier tubing, then there are some issues that will need to be addressed. email me at ctcleanwater@gmail.com for further questions. I will need your phone number or email address to be able to consult with you.
*And I need to add this note; inhibitors will not do the job if the wrong tubing was used.
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