PVC or CPVC pipe can be used for domestic water supply. PEX is typically supplanting this role but PVC is still suitable. However, PVC seems to not be used in hydronic applications although CPVC can be having a higher temperature rating, I believe.
Supposedly one reason for the lack of CPVC in hydronic is that it does not provide a suitable oxygen barrier to protect the components of a typical hydronic heating system, such as cast iron boilers, pumps, brass fittings which may de-zincify, etc.
However I have read contradictory information about PVC materials used in packaging applications, particularly for food, where it's ability to prevent oxygen penetration is specifically cited as a benefit.
So, what are the oxygen barrier capabilities of PVC or CPVC plumbing pipe?
Note - PEX seems far easier to work well for most things. But for cases where large diameter pipe is needed (e.g. 2-in), like in "near boiler" plumbing, PEX isn't as readily available, copper is more pricey, and black iron may be less familiar. So PVC, in theory, would be nice for those cases.