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Odd Water Hammer Noise I Cant Fix

Hi all,
I have a 1900 three floor, 4800 sq Foot home in Detroit. One pipe parallel flow steam heat, with a 10 year old 240K Burnham gas boiler and 22 radiators of all sizes.Thanks to this site and the Holohan books, I have tamed the beast to a mostly quiet and efficient heating system.
I have two noisy spots I can't figure out. Worst, a riser from the second to the third floor hammers moderately when the steam comes up, a problem because the pipe is right behind my bed headboard. A second one is a radiator that hammers badly at the far end of a branch run on the first floor, it is the only unit on that branch.

I have insulated the mains, and have Gorton #2s at the end on all the long mains, and new vents on all of the now properly pitched radiators. The pressuretrol is adjusted about as low as it can go. Attached a drawing with pipe lengths of the basement Layout and vent locations, and where the offending items are located on the floors above. I also attached a photo of the boiler and piping.
I really don't want to tear open the plaster wall where the riser is, and really cant figure out why that would make noise when all of the nearby radiators are quiet.
Reading over again the books and the comments here, do I need to add main vents vents to these branch lines that serve the noisy members? Or is there something else I need to be looking for.
Advice is appreciated. Thanks.


  • Jamie Hall
    Jamie Hall Member Posts: 23,452
    Old houses have a dismaying tendency to settle. And so do the pipes in them. Therefore, the first thing I would do -- assuming you haven't already -- is go over all the piping with a fine tooth comb. And a level. To see if there is any place -- even a short section -- where a pipe which should be pitched to drain back to the main -- or even a main with a sag -- isn't pitched quite properly. It may not be exactly where you are hearing the hammer... One way to help locate the offender, assuming it happens as steam is rising, is to pay attention to just where the steam has gotten to when it happens. That will often localize the problem.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Fred
    Fred Member Posts: 8,542
    Are you sure it is hammer and not the pipe rubbing against a floor board or subfloor or, if in a wall against a wall stud as it expands? Can you record the noise and post it so can hear it?
  • dopey27177
    dopey27177 Member Posts: 887
    You show a drop leg that appears to be 11/2" pipe going into the bottom of the boiler. It is on picture # 2.

    What is this pipe connected to?

  • ChrisJ
    ChrisJ Member Posts: 15,788
    edited March 2020

    You show a drop leg that appears to be 11/2" pipe going into the bottom of the boiler. It is on picture # 2.

    What is this pipe connected to?


    The Equalizer, or the return? Or the gas pipe?

    I'm with @Fred.
    I find it hard to believe a vertical pipe is hammering unless it has a serious amount of condensate dumping down it. Popping as it rubs against wood and expands is far more likely. It would also probably pop slowly over time as it cools and shrinks. But sometimes they don't make noise when cooling. This popping can be very loud, I used to hear a pipe 30 feet away in another room.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment