Contact of dissimilar materials

Okay, everyone knows about galvanized piping and copper piping and the resulting galvanic action that occurs. Dielectric fittings are used to break contact. What about copper water piping and steel Type B flue vents? I’ve seen contractors use cardboard to separate black iron gas piping from copper pipes, but you don’t want to do that since you need to have a min. of 1" clearance to combustibles. Would they have to re-route the copper pipes so they don’t touch? :???: I’ve never witnessed corrosion on these installations. Most are new construction anyway.

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The first thing that comes to mind is, this is a perfect application for asbestos. Yea, I know, don’t go there.

I am trying to think of some sort of non combustable that would do the job. Maybe rock wool, fiberglass.

Hi Hank,

as you stated these dissimilar metals readily react with each other (Copper and Zinc are at the opposite ends of the Galvanic scale). in this instance I would be reporting that due to the close proximity that the copper piping should be re-routed wedging anything between the pipe and the flue is just a bodge and will cause problems down the road.




I agree with re-routing of copper pipes. It is tight in that corner as a total of four gas-fired appliances are connected to a flue vent in that area. I should do another post concerning the omission of combustion air openings for these appliances. Check HVAC thread when you get a chance.

I don’t see any reason why the duct could not have been pulled away from the copper and secured with plumbers strap. If I can’t avoid contact I will wrap the copper with electricians tape were it contacts dissimilar metals.


Those vents are in close proximity to two water heaters and two furnaces with a total of 226,000 Btu input. I think those vents will get hot enough to melt electricians tape or anything non-metallic & combustible for that matter. Vents are rigidly secured in place. Moving those copper pipes looks like the answer.

Do you still see a lot of metal furnace vents in your area? Almost everything I’ve seen in this area that has been installed in the last decade has PVC venting and likely a power vent.

I’ve seen a lot of PVC water heater venting also.

Two different metals on the chimney. Opps
Copper wins galvanized metal loses.