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Copper to black iron

Hi All,

Long time lurker, first time poster. Our place has a older cast iron boiler and really old hot water radiators (nice!). The piping is primarily black iron, but the former owner had some work done, and there is some copper pipe at the boiler. I'll be moving a radiator in the near future, so I'll need to re-run some of the piping. I would prefer to use copper, since I can work with it quite a bit faster. Is there any problems with the transition from copper to iron? In particular galvanic corrosion. Is there anything that should be done to mitigate it? Dielectric unions seem to be frowned upon a bit - the gaskets wear out? The current connections from copper to iron don't appear to be electrically isolated.

Many thanks!



  • Brad White_9
    Brad White_9 Member Posts: 2,440
    Longstanding debate....

    We had a good thread on this about a month ago. My practice is to separate ferrous from non-ferrous metals using a bronze ball valve or nipple. (As you said, stay away from dielectric unions.)
    The bronze acts as a buffer and is resistant to dielectric corrosion in both directions, both from the iron and from the copper. There are plenty of copper to iron joints that have lasted. As one learned poster said, it was because there was something elsewhere in the system that was acting as an anode and being sacrificed instead. Interesting...

    I am speaking of true cast iron versus steel here. Carbon steel pipe and copper will corrode rapidly while a simlar adjacent joint coupling of malleable iron was unfazed. I have seen this where a Weld-O-Let in 2.5" steel necked down to 2-inch steel before transitioning to copper. The Weld-O-Let was destroyed and weeping (as was the Owner!) in about six months of operation. The MI joint was unblemished. That has been my experience anyway.
  • I have no

    I have NO problem using copper with black pipe on heating system... Always use male copper adts into black fittings... No die electric craps ethier.. And make sure no electrical grounding on heating system as some thought it part of the plumbing..
  • ScottMP
    ScottMP Member Posts: 5,884
    I agree

    Have done MANY boiler installs with cast iron headers and copper leads with No Problems. I have also relocated C.I. radiators in homes using male/female adpt.s to the steel piping with no complaints.


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  • ToddInVancouver
    ToddInVancouver Member Posts: 4

    Excellent! Thanks very much for your help, fellows.

This discussion has been closed.