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new radiator - clangs! bad pipe?

Hi folks,

We're just finishing up renovations in our 1906 house. As part of the work, we added a new bathroom on the 3rd (top) floor, with a very small new radiator. This radiator is split off an existing radiator line, which is the end point of that part of the system. As part of the process of installing the radiator pipe, our plumber also rerouted the feed to the old radiator in the split. The new radiator clangs pretty loudly when the system is heating up. We tried shimming it up about 1/4 inch, which helped some. Now it only clangs a few times instead of continuously. Also, I don't know if it's related or not, but the old radiator on the same line is spewing quite a bit of steam. Another detail that may or may not be relevant is that all the radiators in the house were removed when the floors were refinished, and were repainted. So after a bit of research I understand that the whole system may need some re-tuning after being hooked back up. What I'm trying to figure out is if the clanging in the brand new radiator is likely the result of the new piping being laid at an incorrect pitch. If it needs to be fixed it would mean having to rip out the floor in the new bathroom. I'd like to figure this out before our GC is finished with the job so he can be responsible for the floor if necessary. Any advice gladly appreciated! Thanks steam heating mavens.


  • Jim Pompetti
    Jim Pompetti Member Posts: 552

    one pipe or two. I  would NEVER have split the pipe
  • Jamie Hall
    Jamie Hall Member Posts: 20,857
    Clang on startup

    Somewhere the condensate being formed in the pipes as the steam starts to come into the pipes is not able to drip back to where it belongs (no matter whether one or two pipe -- during that interval there will be a time when there is a counterflow in the feed to the radiator).  Which is a pitch problem and possibly a size problem.  If there are any horizontal runouts on that new radiator, that's the first place I'd look, both for pitch and size.  Remember that just because a vertical pipe may be big enough, it doesn't mean a horizontal one is.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • mofuzz
    mofuzz Member Posts: 3

    It's a 1 pipe system, sorry should have mentioned. Also, to clarify, the new horizontal pipe is split off the vertical pipe, not the horizontal that fed the old radiator. Is there a better way it should have been done?

    Unfortunately, all the horizontal pipes the plumber laid are under the floor, so there's no easy way to check size or pitch without opening the floor. :-(

    Are there other things that we could try or check without having to resort to demolishing new construction?
  • Jamie Hall
    Jamie Hall Member Posts: 20,857
    I can think

    of at least one really evil scenario -- that new pipe, where it comes off, comes off with a T rather than a 45 -- and condensate from the one radiator is getting into the runout to the other, and going whang...

    But my money would be on the new horizontal itself -- either too small (for instance, 1" will only take 28 square feet) or too little pitch (half inch per foot, minimum).
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Paul Fredricks_3
    Paul Fredricks_3 Member Posts: 1,557

    You said you shimmed the radiator 1/4" and it helped a bit. If you mean you shimmed the entire radiator up 1/4" and that helped, sure sounds like a pitch problem. Can you shim it up more? I mean, without breaking anything?
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