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Steam Hammering after re-work

Hi all,

I have lived in houses with steam heat for many years. I understand the principles but have not had time to fine tune my system. The question I have relates to the WORST steam hammering I have ever heard. This summer we finished our 1930's era basement. We hired a large, well known local mechanical contractor to do the steam pipe work. I have three concerns, which I spoke to the tech about before the install;

-Originally there was a steam line around the perimeter of the basement wall on the front and right sides of the house. It was about 8" below the floor joists and 18" from the wall. We made a bulkhead around the front portion of line and rerouted the right side portion to run flush to the wall behind a 2"x4" stud false wall. The line also had to be routed DOWN to clear a window it previously ran in front of. So the line now has a 90 L toward the ground at the wall and a 90 L towards the rear. It then T-s to a vertical line to a 2nd floor radiator. This vertical line also continues to and under the basement floor back to the boiler.

-Originally where the perimeter line connected to the vertical line that runs to the 2nd floor radiator there was an air valve. When the lines were reconfigured they did not install a new air valve.

-Insulation was not installed on the new lines (one of which is now flush with the basement exterior wall) when they were installed.

I questioned the tech about each concern (change in pitch of steam line, elimination of air valve and insulation) before the install and was assured that there would be no problems.

Was this job done correctly? If so, why else would I have this hammering that I never had before?

If the work was not done correctly and warranty repairs are required, should I expect the mechanical contractor to cover the expenses of removing and replacing the new studs, drywall, paint, etc? I would want to use the carpenter who finished the basement.

Please let me know if you have questions that I can answer in order to help.

Thanks in advance.



  • thefloydthefloyd Member Posts: 6
    edited December 2010

    Sounds like a single pipe steam system, correct? I'd be very wary of the change of level of that steam pipe around the window. I'm assuming once the main is dropped from its previous height to the new height it continues around the basement at the new height? (IE: the new under the window height) and then drops to the floor at some point and is piped back into the boiler?

    I'd be very concerned that the change in height significantly decreased your "A" dimension, or the amount of vertical pipe height between the end of the horizontal main and the water level in the boiler. Depending on your system, you normally need a minimum of 28" of "A" dimension in a single pipe gravity return system. If your "A" dimension is too short, condensate will back up into your horizontal steam main and when the steam comes around and hits that water it'll hammer like mad.

    If your "A" dimension is still large enough (I doubt it is, but maybe) - I'd check the pitch on those pipes next.

    Also, after re-reading your post it looks like after that window & drop, the next "T" goes both vertical up to a radiator and down back to the boiler but there's no air vent? That's bad news too. You're essentially venting your entire main steam line through that singular radiator at the end of the line.

    That main and the near boiler piping should ALL be insulated. Heat loss from uninsulated pipe is HUGE and will cause large amounts of condensate to form along the main (instead of in the radiators where it should be forming).

    Unless I'm misunderstanding (please correct me if I am) it sounds like that guy who did your work made several big mistakes.

    I, too, have a finished basement (the previous owners finished the basement) and they were smart enough to leave the steam pipe alone - sadly it runs right down the middle of my window, but I surely don't have any hammering.
  • CravacorCravacor Member Posts: 2

    I met with the mechanical contractor today (I met with the general manager of the company) and described my problem. His response was that there may be a balance or leaking valve issue since I have 2 radiators shut off all the time. He recommend that I have any old or faulty air vents on the radiators replaced, then adjust them so I am getting the desired heat in each room. He thinks that if I have one or more radiator shut off there may be an issue with a leaky valve. This makes sense but doesn't explain why I didn't have the hammering issue before the rework. I know the system needs to be checked and balanced anyway so I am going to do this first. In addition, I think that once this is done if I still have an issue it will be a clear indicator that the rework is causing the problem. The tech will be here Friday to check and replace the air vents. Anything I should be aware of when they vents are replaced? I know the vents themselves should not cost over $20 each, but I would appreciate any other knowledge that will be helpful to me as regards the vent replacement and balancing.

    Thanks again!
  • Charlie from wmassCharlie from wmass Member Posts: 4,123
    Good ones cost more but we

    do not talk price here as it varies by area. Did they provide a drip when they dropped the line under the window?
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • World PlumberWorld Plumber Member Posts: 389
    New pipe

    No mention of the boiler water. Is the water in the boiler bouncing a lot? Is it black and oily? Was the boiler run then skimmed after the oil came back from the new pipe? How much did they drop the pipe? As mentioned above the "A" and "B" dementions  need to be there or water will be drawn into the pipe and cause hammering. Did they maintain the pitch back to the return or the boiler? An sag in the pipe will collect condensate. Lack of main vents will give you a poor preforming system and burn a lot of extra fuel. Non insullated pipe will take longer to heat up and take longer for steam to move in it. Will give you more heat in the basement.

        If you get on of the steam books and look at the dementions and how it should be done you can compare and know what to ask for. The Tee you mentioned being dropped. How much higher is it than the water level in the boiler? Are you getting heat in that radiator? If not the return water could be pushing up int the tee and blocking it off and causing the hammer?

        If they did the piping right it might be oil in the water causing wet steam and thus the hammering. That could be remedied by having the boiler skimmed. If that's the problem you should be able to see the water jumping/bouncing in the sight glass when the boiler is running.
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