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When connecting copper to steel do you need to use dielectric unions. I was told by an engineer that electrolysis does not exist in a heating system. I have tried to research this topic but have been unable to find any information supporting the engineers answer. Thank you.


  • GroundUp
    GroundUp Member Posts: 1,905
    With a closed system, electrolysis is nothing but a facade. A lot of makeup water will create issues without dielectric fittings, but a standard residential system dielectric fittings are nothing but trouble IMO
  • Jamie Hall
    Jamie Hall Member Posts: 23,275
    Well, yes and no. Electrolysis will exist anytime two dissimilar metals are in contact with the same electrolyte and also electrically connected. Is it a problem in heating systems? Not really, by all the evidence.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • hot_rod
    hot_rod Member Posts: 22,114
    Yes even similar metals can support electrolysis, old copper to new copper even, according to the Copper Development Association

    Water with high TDS increases the “electrolyte” and the potential for electrolysis

    In closed loop, sealed Hydronics the mixed metals should not be a concern

    Adding a hydronic condition help protect all the metals also if you are concerned.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream