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Noisy risers and radiators

Recently installed a Weil McClain 880 boiler in a 15 unit 5 story coop apartment building with approximately 50 radiators. Originally had water hammer at piping next to the boiler and a constant feed of fresh water in the boiler during the cycling resulting in a extremely high water level. We flushed the boiler numerous times over the next two weeks to clean out the system and the technician increased the psi cutoff from 2.5 to 5 psi. After those actions the hammer stopped and water level stablized. We are currently experiencing loud pinging sounds from a few risers during the start and end of the heat cycle and the sound of dripping within the risers after the heating cycle. The dripping sounds like water hitting a hardwood floor. No leak has been detected, which makes me believe it is within the riser. The air valves on many radiators hiss loudly on both the start and end of the heating cycle, the start sounding more wet and the end sounding dry. The building is very warm and some tenants don't open their radiators at all, especially on the top floor, the building historically has always been warm. We plan on changing all the air valves and try to balance the system, but prior to that I hope to be able to understand the current situation better. I'd also like to reduce the psi cutoff back down to 2.5 psi if possible. It currently reaches about 4.5 psi during the heating cycle. In addition the system lacks steam traps. Any insights?


  • Gordan
    Gordan Member Posts: 891
    Expansion noises?

    Sounds like the piping is binding at penetrations.
  • MikeBlue
    MikeBlue Member Posts: 9
    Expansion noises

    Can you explain. Are the pipes expanding and contracting as they heat and cool? and if so, why does it happen to some and not to others?
  • Jamie Hall
    Jamie Hall Member Posts: 22,934

    reduce your pressure down to no more than 2 psi cutout.  Any more than that is going to fry your vents sooner or later, and does nothing for the heat other than make your fuel supplier very happy.

    The vents hiss at the beginning of the cycle because they are releasing air.  Some vents hiss more than others; depends on the make and the size (and, I sometimes think, the phase of the moon...).  They hiss at the end of the cycle because they are letting air back in as the system cools.  Both hisses make me wonder if you have main vents and, if you do, if they are large enough.  Can you clarify that for us?

    The hammer stopped most likely because of correcting the water level and cleaning the boiler -- both of which will reduce the water carry over with the steam.  Not because of the pressure change.

    Expansion noises often can be difficult to pin down.  Such things as a pipe leaning fairly hard on a piece of wood somewhere will do it.  Some radiators (particularly longer ones) often ping a little bit.  You sort of have to go around and figure out where the noise is coming from, and then what is causing it.  Can't give you an exact answer on that.

    Dripping in the risers may be just exactly that -- particularly if you are not having to add much water to the boiler.

    No steam traps?  You may not need them -- many one pipe systems are piped in such a way that they are not needed.  If the system is heating the building OK, which it sounds as though it is, it would seem that they aren't on this.  We would need to have a fairly complete diagram of the piping, though, to be sure.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • MikeBlue
    MikeBlue Member Posts: 9
    edited December 2010
    Main Vents

    Thanks for your help. Our main divides into three lines and each has one Gorton #1 vent right before they meet the risers. As I metioned earlier, I am going to replace all the valves in the system as soon as I feel I have a good understanding of the sizing I need. I've seen examples of the Gorton's #1's clustered together, is this something I need to consider? All the risers end with the radiators on the fifth floor. But two out of 3 of the apartments on that floor keep their radiators turned off since the building is relatively hot. Thanks for your advice.
  • Steve_175
    Steve_175 Member Posts: 238
    Vent Size

    Three Gorton #1's are equal to one Gorton #2 and will cost more than just one of the # 2's.

    Considering the size of your building you may need even more than one #2 per main. How long is each main?

    Also and I am speculating here, you may have vents at the top of your risers. Have you ever followed the risers to see how they terminate at the top of the building?

    Your dripping may be due to a level horizontal  pipe that fills up with condensate and slowly drains back. Just a guess.

    Can you post some pics of the system?
  • overfeeding

    definitely lower that pressure, to below 2 psi, for function, or 12 ounces for comfort and economy. lower pressure will also lower the surface temperature of the rads and pipes, and perhaps reduce the amount of metal expansion causing the noisy riser.

    also why not turn off the auto-fill and see if you have any water loss.

    the more you can do to let the air out of the mains and risers quickly, the better. pex supply.com has a discount for vents by the dozen, and you may well need to put on that many by the time you have every thing finished. this where a good low pressure gauge comes in handy, to show the back pressure, as the building of steam in the boiler, is pushing against the ease of air escape from the main vents. the difference is  the back-pressure, and you want it to be as low as possible [mine is 2 ounces!]. by watching the change of pressure as the mains are filled with steam first, and then the risers, you can get a good idea of when you have enough venting.--nbc
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