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Dielectric unions

MikeL_2
MikeL_2 Member Posts: 369
I spoke with rheem tech support today regarding a heat pump water heater install that we'll be doing this week. They do not require dielectric unions, but was wondering if there were any advantage using them?

Comments

  • hot_rod
    hot_rod Member Posts: 16,272
    MikeL_2 said:

    I spoke with rheem tech support today regarding a heat pump water heater install that we'll be doing this week. They do not require dielectric unions, but was wondering if there were any advantage using them?

    Nope, none whatsoever.
    Use a copper or stainless flex to furnish the required union connection. Or a rubber/polymer version to help eliminate vibration transfer.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    mattmia2
  • unclejohn
    unclejohn Member Posts: 1,757
    Dielectric union is French for this will leak soon.
    Solid_Fuel_ManCTOilHeatCanuckerCBRob
  • Big Ed_4
    Big Ed_4 Member Posts: 1,882
    When do you recommend using Dielectric unions ? I always thought they are used to protect the tank ?
    I have enough experience to know , that I dont know it all
  • GroundUp
    GroundUp Member Posts: 1,398
    Big Ed_4 said:

    When do you recommend using Dielectric unions ? I always thought they are used to protect the tank ?

    Never.
    rick in AlaskaSolid_Fuel_ManCanuckerfenkel
  • hot_rod
    hot_rod Member Posts: 16,272
    The dielectric unions are designed to stop the current flow that causes electrolysis. Two dis-similar metals in the presence of an electrolyte (water) can react and the less nobel metal will deteriorate.

    Softened water has additional conductivity and more potential.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Big Ed_4
    Big Ed_4 Member Posts: 1,882
    What about the connection between lets say a Bosch boiler and a iron manifold .. Where the connection out of the boiler is copper ?
    I have enough experience to know , that I dont know it all
  • hot_rod
    hot_rod Member Posts: 16,272
    My experience is dielectrics on boilers cause more problems than they solve. Boilers are typically closed systems no constant source of electrolyte.

    One reason why DI or filtered water is recommended for hydronic fills, if all or most of the ions are stripped out the potential for electrolysis is eliminated.

    Here is some reading from Idronics 18

    Water heater tanks get their protection from the anode rods.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Canuckermattmia2fenkel
  • Big Ed_4
    Big Ed_4 Member Posts: 1,882
    Thank You for the time of explaining to me
    I have enough experience to know , that I dont know it all
  • jumper
    jumper Member Posts: 1,827
    hot_rod said:

    My experience is dielectrics on boilers cause more problems than they solve. Boilers are typically closed systems no constant source of electrolyte.

    One reason why DI or filtered water is recommended for hydronic fills, if all or most of the ions are stripped out the potential for electrolysis is eliminated.

    Decades ago I offered to fill hydronic systems with conditioned water. Most potential customers did not want to give up automatic water make up. Didn't even want to pay for side stream DI service. Years later when scale built up the problem became that cities object to flushing treated waterdown drains or on pavement.
    Even when there is a water meter on make up nobody faithfully logged.

    fenkel
  • Intplm.
    Intplm. Member Posts: 1,375
    @MikeL_2 . In your case, you probably do not need dielectric unions. Most heat pump water heaters supply dielectric nipples installed at the cold and hot threads on the water heater. This is usually enough to help prevent electrolysis from occurring.
    delta T
  • MikeL_2
    MikeL_2 Member Posts: 369
    Thank you, everyone for your contribution / information. As usual, the experiences and shared knowledge provide an opportunity for learning, and paths to pursue.
  • mattmia2
    mattmia2 Member Posts: 5,505
    I didn't think about it as the anode protects the tank AND the connections, but it does.

    You can fill the system with deionized water and hook it up to a prv to add the small amount of water the system would lose. It would still keep the water relatively demineralized.
  • gennady
    gennady Member Posts: 832
    edited March 2020
    Dielectric unions will leak. The only question is when. Brass fitting or valve is the best dielectric to separate dissimilar materials. To protect hot water heaters you need to inspect and replace anodes as needed.