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Radiator Pipe Finish

I'm slowly going through the heating system in our home that is 100 years old.  It was an old steam system, converted to a 2 pipe Hot Water closed loop system with a pump.  I'm having the radiators sandblasted to bring back the detail work that has been painted over for years.

As I restore each radiator, I will need to replace some of the piping.  I'm replacing the piping back to each valve in the room and then when we replace our boiler, I'm going to have the rest of the pipework back to the boiler replace and zones configured. 

I'm trying to figure out what type of steel pipe to get, black or galvanized?  I'm a mechanical engineer and fairly familiar with the corrosion protection that the zinc provides to the steel pipes, but I haven't been able to find any conclusive answers as to why this is not typically used for radiant heat piping?

My thoughts are that the zinc will galvanically sacrifice itself because the regular black pipe corrodes at such a slow rate due to the closed loop system.  What are the issues with using galvanized steel pipe in this type of arrangement?  Will the zinc in the water cause any issues with the boiler or pump?  Our city water is very hard with a significant amount of iron. 

Any thoughts are greatly appreciated.




  • Charlie from wmass
    Charlie from wmass Member Posts: 4,322
    I find

    Black iron on hot water will last 100 years if there are no leaks allowing in fresh water and air. Galvanized pipe and fitting seem to be of quite poor quality under the zinc. I know with steam systems the zinc can peel off and cause issues as it does with gas piping. This sounds like a good summer project where a professional comes in and does it all even in copper if you are looking to zone. or even in pex back to home run manifolds with a variable speed circulator.
    Cost is what you spend , value is what you get.

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  • meplumber
    meplumber Member Posts: 678
    I have seen some pretty ugly things inside galvanized pipe.

    Also a note.  The zinc reacts horribly with glycol antifreeze and some of the boiler chemicals in use.

    I agree with Charlie.  I have seen 100+ yr old black iron systems that were still in good shape.  When I see galvanized pipe or fittings, I try to remove them if possible.  As Charlie stated, the quality of the pipe under the galv coating tends to be pretty poor.

    Good Luck.
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