Most oxygen-barrier PEX does not have the appropriate approval codes for use with potable water and should not be installed in domestic plumbing applications. Uponor’s hePEX recently received NSF approval, making it one of the few types of oxygen-barrier PEX on the market that can also handle domestic water.
Fresh oxygen causes ferrous metal components (cast iron circulator pumps, boilers, etc.) to rust in hydronic heating systems. Since oxygen from the air can penetrate PEX tubing (even when the PEX is embedded in a concrete slab), an oxygen barrier is needed in most heating systems. The aluminum layer serves as the barrier in PEX-AL-PEX tubing, while a layer of ethylene vinyl alcohol (EVOH) is applied to the outer layer of standard oxygen-barrier PEX. This layer normally makes the tubing unsafe for potable systems, but this is no longer the case with hePEX tubing.
Current hePEX tubing carries cNSFus pw-rfh ASTM F876/877 and PEX 5006 ratings stamped on the tubing. Older hePEX was manufactured with the same formula and would be safe in potable systems. Now you can use extra hePEX tubing from a heating job on your next plumbing project or buy hePEX coils to meet all your PEX tubing needs. As always hePEX carries the PEX-A grade, making it more flexible and easier to work with than PEX-B and PEX-C pipe. PEX-A pipe also offers added freeze-resistance, compatibility with expansion-style fittings, and the opportunity to fix kinks by applying heat.