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Thread: Dielectric between black pipe and copper?

  1. #1

    Default Dielectric between black pipe and copper?

    I have hydronic heating. The boiler has black pipe coming out of it. Do I need some kind of dielectric between that and my copper pipe?

    I was also noticing that the flange on my pump is cast iron and I was going to connected it to the copper. Do I need some isolation there (like put a bronze valve)?


  2. #2


    Yes, you will need a di-electric between those different metals if you are to combat electrolysis at this point. Your flanged connections at the pump may have some protection built in but additional protection is not a bad idea.
    Good Luck to you. calsplumbingonline.com
    Cal's Plumbing Online

  3. #3
    Master Plumber nhmaster's Avatar
    Join Date
    Jul 2008
    S. Maine


    I've been transitioning from cast to copper on boilers for years with no dielectric union and never had an electroloysis problem. Are you saying that when you pipe copper off a Cast iron boiler you use a dielectric union?

  4. #4


    Yeah I had heard it both ways. I had done a bunch of searching and I never could find any definitive data.

    Right now I am thinking of just hooking the copper straight up to the boiler. I didn't really like the idea of using one of those dielectric unions either.


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