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Plummer used PEX-B when he replaced our indirect water heater, is this wrong?

We had our old Vaughn Top Performer 70 Gallon Indirect water heater replaced. Since it lasted us 22 years and worked well we went with the same unit since they still make it. However, this time our plumber connected all connections to the top of the tank with PEX-B and then used PEX to copper fittings to connect back to the existing 4 copper pipes (from furnace, to furnace, cold water feed, hot-water output).

Just curious if the use of PEX is correct in this install? Again it is an indirect hotwater heater which doesn't make heat just more of a holding tank with no combustion or heat source.

Thank you in advance.


  • mattmia2
    mattmia2 Member Posts: 9,747
    It is fine as long as the type of pex b used on the boiler side has an oxygen barrier unless there is some specific local code prohibition.
  • HomerJSmith
    HomerJSmith Member Posts: 2,468
    pex b used on the boiler side has an oxygen barrier
    Why such a large capacity indirect? Regulated by a sensor or aquastat? Do you have a thermostatic mixing valve on the supply of hot water to the faucets?
  • Ironman
    Ironman Member Posts: 7,379
    edited August 2023
    Does the pex say O2 or Oxygen barrier on the markings?

    I’ve yet to see any pex B with an O2 barrier in our area.

    You’re also not supposed to connect pex directly to a water heater. It should have 18” of non ferrous metal piping before transitioning to pex.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • mikedo
    mikedo Member Posts: 174
    what is the reason for not connecting pex directly to a water heater
  • GGross
    GGross Member Posts: 1,070
    If the pex is on the boiler side of the indirect it needs to have an oxygen barrier (it will usually be written somewhere on the pipe, "barrier" or something similar), if it is on the plumbing side it doesn't need an oxygen barrier. Pex-b is not enough information to discern if this is the correct application for the product unfortunately, as pex-b comes in both barrier and non-barrier styles
  • ChrisJ
    ChrisJ Member Posts: 15,784
    mikedo said:

    what is the reason for not connecting pex directly to a water heater

    Normal heaters, I think the rule is in place to keep people from putting pex right next to a drafthood.
    Uponor allows it to be installed directly to electric heaters etc, but not next to a drafthood.

    Code in many areas still won't allow it due to the possibility of someone misunderstanding the rules.

    That's the understanding I have of it. None of this applies to an indirect.
    Pex can handle I think, up to 200F at some reasonable pressure.

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,110
    Please post a picture, I'd like to see the install before commenting.  Pex may be rated for 200 degrees but I've seen it get soft passed 180...a bit discomfiting.  Mad Dog 🐕 
    EBEBRATT-Ed Member Posts: 15,624
    An indirect at 120-130 shouldn't be a problem with pex.

    I don't understand if the original Vaughn indirect was replaced with the exact same model why didn't the plumber just stay with copper?

    Seens like more work to install pex although maybe the pipe alignment changed in 22 years
    Mad Dog_2Alan (California Radiant) Forbes
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,110
    Yes Of course on the temps.  Exactly what I'm thinking Ed, sounding like a Frankenstein install.  I've seen that some guys,  once they go PEX or Press, will use it exclusively, even where its really not called for or appropriate. I'd just like to see a photo.  Mad Dog 🐕 
  • hot_rod
    hot_rod Member Posts: 22,260
    Pex will be able to handle the pressure and temperature. It reduced flow rates a bit with smaller inside diameter.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • iced98lx
    iced98lx Member Posts: 68
    In my neck of the woods you can install pex right up to an indirect or electric water heater, but it must be 18 inches from the heater for gas, so this would be fine (again, in my neck of the woods, not everywhere).

    As far as oxygen barrier vs not, for the two pipes connecting the home potable water supply (cold in, hot out to the house) don't need to be (in my understanding) but the two going to and from the boiler (which runs through a heat exchanger in the indirect) should be oxygen barrier so that you are not introducing air into your boiler loop. Will 4 feet of pex b introduce enough air to cause major problems? I can't say, but it's not proper.

    Around here even Menards (big box store) sells barrier pex for heating applications.

    I'd check the pipes and see if you can see any markings to suggest it's barrier and then just simply reach out to your plumber and ask nicely. "Hey, I can't tell if this pex is oxygen barrier where it ties into the boiler, can you clarify for me if that was used as it is my understanding it needs to be.."
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,050
    edited September 2023
    Since it lasted us 22 years and worked well we went with the same unit since they still make it.
    Spend a bit more and the indirect will outlast you. Other brands have a lifetime warranty.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab