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Water hammer sound one only one of two radiators

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Hi, I recently moved into the second floor of an typical old NYC apartment building. When the bedroom radiator starts up, there is an extremely loud clanking sound. It seems to be strongest in the pipe going from floor to ceiling and not really the radiator itself. The living room radiator is nearly silent and also heats quickly, the bedroom radiator that clanks doesn't heat as quickly. In addition, the steam vent releases water occasionally, reaching three feet above. I've also made sure that the radiator is pitched downward. Would replacing my steam air vent fix at least the water spray issue?

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  • Jamie Hall
    Jamie Hall Member Posts: 23,536
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    That's not a venting problem. Somewhere in the pipe going to that radiator there is a spot where the condensate can't drain. It may be a very short section of horizontal pipe pitched the wrong way -- or it could also be as simple as the valve not all the way open or partly failed so that the flow of condensate is blocked.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • danieln93
    danieln93 Member Posts: 3
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    That's not a venting problem. Somewhere in the pipe going to that radiator there is a spot where the condensate can't drain. It may be a very short section of horizontal pipe pitched the wrong way -- or it could also be as simple as the valve not all the way open or partly failed so that the flow of condensate is blocked.


    Thank you for your reply, that’s interesting because the one radiator that works perfectly fine has a pipe that more or less runs straight as opposed to the one above. 
  • pedmec
    pedmec Member Posts: 994
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    Check to make sure the radiator valve is opened all the way. You can't throttle a radiator valve on a one pipe steam system. Either all the way open or all the way closed.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
    edited November 2022
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    danieln93 said:



    That's not a venting problem. Somewhere in the pipe going to that radiator there is a spot where the condensate can't drain. It may be a very short section of horizontal pipe pitched the wrong way -- or it could also be as simple as the valve not all the way open or partly failed so that the flow of condensate is blocked.



    Thank you for your reply, that’s interesting because the one radiator that works perfectly fine has a pipe that more or less runs straight as opposed to the one above

    Is this a picture of the noisy radiator or the quiet radiator?

    The problem may also be in the radiator above you or below you. The noise can travel thru the pipes and you are hearing something that is happening many feet away.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • mattmia2
    mattmia2 Member Posts: 9,837
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    Does all of that piping toward the wall all pitch downward? It is possible that all that piping is pushing the piping below the floor down so that it is sloping the wrong way and trapping condensate.
  • neilc
    neilc Member Posts: 2,711
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    is that a steam valve?
    or a water valve?

    and is that radiator floating off the floor at this end?
    is the other end at a higher pitch ?
    rad needs to pitch so water returns back thru the valve
    known to beat dead horses
    mattmia2
  • Jamie Hall
    Jamie Hall Member Posts: 23,536
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    I'm a little concerned about the pitch of the pipe coming out of the wall -- is it sloped adequately to drain back to the riser?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    mattmia2
  • danieln93
    danieln93 Member Posts: 3
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    I'm a little concerned about the pitch of the pipe coming out of the wall -- is it sloped adequately to drain back to the riser?

    Hopefully this is a better angle. It is floating on this end but is elevated slightly on the other side. Assuming that I should have it supported on both sides, still elevating the other side for starters?
  • mattmia2
    mattmia2 Member Posts: 9,837
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    Especially if it is resting on that pipe out of the floor it may be pushing something below down so that it is sloping the wrong way. I would support that end and maybe try raising it a little.
  • neilc
    neilc Member Posts: 2,711
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    looks even worse now in this pic,
    raise the whole rad gently, set a lever under its middle,
    you probably want a helper to hold and stabilize the rad while lifting,
    get shim, or block of wood, under those rad feet on this valve end,
    (so even the valve starts to pitch back to the 90 to wall/floor),
    this may raise the pipe thru the floor, so have differing blocks available,
    it all wants to pitch back to the floor/boiler,
    and then the other end or the rad also wants to, shall pitch, to the valve end,
    known to beat dead horses
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
    edited November 2022
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    Illustration of what @neilc said.

    The picture looks like the pipes are pitched in the wrong direction. But that may just be the angle of the camera. The red arrow should be pointing down hill so condensation (water) can drain back out of the radiator. In this picture, it appears to be pitched up to the wall not down.

    The highest part of that set up is the bottom of the far end of the radiator should be the highest point so the water drains back out of the radiator to the pipe then back down to the boiler room.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
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    Of course, after you fix your radiator's slope, the radiator above you may end up being pitched the wrong way, so that apartment will inherit the noise. Don't you just love old steam systems?

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • neilc
    neilc Member Posts: 2,711
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    maybe rad and pipe can be adjusted just there in the room,
    without pulling the pipe up thru the floor, a little index mark on the floor pipe could be telling,
    maybe some gentle , judicious application of wrenches there at the floor to rad piping,
    known to beat dead horses