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Water hammer in one pipe system on cold start

Jon47 Member Posts: 5
I've got a one pipe steam system in my 1947 cape style home

I have a radiator in one of my upstairs bedrooms that consistently pounds and hammers when ever the heat turns on first thing in the morning. For example, when we goto bed the heat turns off for a few hours and then as we wake up the heat turns back on. When it turns on after it has been off for a while this radiator POUNDS and wakes us up before our alarm even goes off.

Not only that, but water is spewing out of the valve on this radiator as well. The rad is properly pitched, so I am confused as to why this would be occurring. It seems that once the system warms up, the hammer no longer occurs. But we can still hear water rushing through the pipes in our walls as if it was a forced hot water heating system

Does anyone have any ideas as to why this would Be happening?


  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,576
    Is this your house&system, or an apartment?

    This is probably due to a system wide problem, with excessive pressure. Can you do anything about that or are you renting?--NBC
  • Mark N
    Mark N Member Posts: 1,115
    edited January 2014

    Are you using a set back overnight? If so how much. Steam is better left at one temp. What do you have the vent set for. That is a convector not a radiator. It doesn't hold much air. Slow the venting down, if you vent too fast the condensate can't drain against the incoming steam and will bang. Also make sure the hand valve is completely open.
  • JohnNY
    JohnNY Member Posts: 3,226

    Fin tube and 1-pipe steam are a terrible combination and what's in that picture does not inspire confidence that whoever's been working with your system is knowledgeable about steam heat.

    You need someone good to look over your entire system.
    Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
    Consulting & Troubleshooting
    Heating in NYC or NJ.
  • JStar
    JStar Member Posts: 2,752

    Looks like the 1-1/4" BB is reducing at a 1" supply. Well, there's your problem!
  • Jon47
    Jon47 Member Posts: 5


    The pressuretrol is set to .5 psi (as low as it can go), I don't how else I would be able to manage the pressure involved here. Any ideas?


    I have a set back overnight yes. Most of the day the temperature in the house doesnt drop below ~64 degrees, and then at night (while we sleep) I have it set to 59 degrees. I have the thermostat kick back on around 7am to heat the house back up in the morning to 65 degrees. It is at that 7am start that the water hammer and surging gets really bad. Are you suggesting that I keep the thermostat at a more consistent temp throughout the night?


    Would you suggest that I look to replace this fin-tube with a more appropriate cast iron radiator? This isn't the only one in the house that is built like this, but this is the only one that is really problematic. I have 2 larger fin-tubes on my first floor that have generally performed pretty well so far.


    Are you suggesting that the pipe in the fin-tube is too large for the supply valve that is installed here? What if I update the supply to be 1-1/4" so that is consistent? Do you think that would make a difference?
  • Mark N
    Mark N Member Posts: 1,115

    Does it only bang during the recovery from set back? Leave it a 64 for a few nights and see what happens.