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brass or dielectric unions for stainless indirect to copper boiler piping

We used to use Munchkin's, and their stainless water heaters. As I recall, they insisted we not use di-electric unions on the boiler connections.

Now we have switched to Lochinvar, and their stainless steel water heaters. The manufacturer's rep say they don't care between brass and di-electric unions. I would like to utilize best practice here, but I don't know which is better between the two. The fittings are stainless mail nipples at the water heater indirect loop, going to the copper piping to/from the boiler.

What is the best way to proceed?

Comments

  • bmwpowere36m3
    bmwpowere36m3 Member Posts: 512
    Based on my reading.... many people complain that the dielectric union itself rusts out or that the rubber seal within it degrades. Basically causes more problems then it solves.

    SS and copper can live happily together.
    thoughtfulTomicesailorAlCorelliNY
  • Larry_52
    Larry_52 Member Posts: 181
    304 or better 316 are in the cathodic range and with copper the potential between the two is small, even in a constant electrolyte. Brass will be the anode especially yellow brass with stainless. The lower the zinc content in the brass alloy the less problems possible. Will really depend on your water TDS and gases to know how aggressive the galvanic corrosion will be in this scenario. if lockhnivar isn't concerned then I would not worry. Dielectric unions be more of a headache down the road than the actual corrosion you are trying to stop.
    thoughtfulTom
  • SWEI
    SWEI Member Posts: 7,356
    This is on the boiler side, not the DHW side, correct?
  • icesailor
    icesailor Member Posts: 7,265
    Someone stole my digital camera with all my digital photos of leaking dialectic unions on LPG services from underground tanks. WHile I was walking around a house I was turning the water in in the spring, I would catch a whiff of Mercaptan and my nose would lead me right to the regulator. The unions were always AFTER the tank and before the regulators so I could shut them off.
  • thoughtfulTom
    thoughtfulTom Member Posts: 18
    SWEI - this is on the To/from boiler connections for the heat exchanger coil inside the water heater, the connections are at the water heater - male stainless stub-outs.
  • SWEI
    SWEI Member Posts: 7,356
    As long as you keep the system airtight, pretty much anything will work.

    On the domestic side, as pointed out above, stainless and copper are fine together. Dielectric unions fail. A lot. We avoid them like the plague. If there is a genuine need for dielectric isolation, a foot or two of PEX or Aquatherm will do the job far better.
    thoughtfulTomLarry_52
  • AlCorelliNY
    AlCorelliNY Member Posts: 63
    We also avoid dielectric unions.
    Unless you want to make service calls for the future. Easy to diagnose. Just walk in and point to the dielectric union.
    Al Corelli

  • RobG
    RobG Member Posts: 1,850
    SWEI said:

    As long as you keep the system airtight, pretty much anything will work.

    On the domestic side, as pointed out above, stainless and copper are fine together. Dielectric unions fail. A lot. We avoid them like the plague. If there is a genuine need for dielectric isolation, a foot or two of PEX or Aquatherm will do the job far better.

    Try explaining that to the ME.
  • Weezbo
    Weezbo Member Posts: 6,232
    Die electric unions do just that , they die.
    Unless a requirement go with dezincified brass or copper.
  • icesailor
    icesailor Member Posts: 7,265
    RobG said:

    SWEI said:

    As long as you keep the system airtight, pretty much anything will work.

    On the domestic side, as pointed out above, stainless and copper are fine together. Dielectric unions fail. A lot. We avoid them like the plague. If there is a genuine need for dielectric isolation, a foot or two of PEX or Aquatherm will do the job far better.

    Try explaining that to the ME.
    That's because they're smart and overeducated. We're not.