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Weird water hammer in one radiator

Dsisson Member Posts: 94
edited February 2023 in Strictly Steam
I have a large house (about 6700 SF) with a Weil McLain 80 series boiler. 1908 house. Total of approximately 29 radiators which include typical above floor radiators and about 9 underfloor radiators ("forced air" with a ducted fan system)

One radiator has some water hammer - actually, a glug glug glug sound. This sound starts after the radiator is about halfway heated across, and stops once the radiator is fully hot. OF COURSE this is the only radiator with the problem and ALSO is the radiator in my bedroom. None of the other radiators have this issue.

For efficiency reasons, I've shut off radiators in unused rooms. If I open these radiators back up, the offending radiator stops the offending sounds.

The offending radiator is sloped in the correct direction and the valve is fully open. It has a ventrite adjustable valve on it. If I nearly close the ventrite (about 2 or 3) the sound does go away, but then the room is cold.

Obviously, I can get rid of the sound by opening up other radiators, but I'm worried about WHY it's making the noise. Is the return partly clogged or ?? for example.

Other data: the boiler has a vaporstat set at 8 ounces cut out and I think about 2 OZ cut in and has a good long firing time before it hits 8 OZ. Some of the mains and also underfloor radiators have F&T traps which all seem to be working OK, but I'm not very familiar with F&T traps.


  • Jamie Hall
    Jamie Hall Member Posts: 23,543
    In a sense you are probably right -- partially clogged runout (since this is one pipe, your runout is both supply and return). But the question is -- with what? Since you can get it to stop by opening the valves on other radiators, clearly it's not a physical clog -- but it's very likely that it is slugs of condensate from the other radiators appearing and accumulating from time to time. It is very important to remember that closing the supply valve on a one pipe radiator does not completely prevent steam from getting into it, although it may come close. The inlet valves are not intended to do that.

    You may be able to locate a place in the piping to the various radiators in question where there is inadequate -- or even slightly reversed -- pitch. That would be a good place to start.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Waher
    Waher Member Posts: 256
    edited February 2023
    Shutting off steam radiators doesn't increase efficiency. Your boiler is making the same volume of steam regardless of what valves are open until the thermostat is satisfied. If you want to increase efficiency that's an exercise in insulating distribution piping, adjusting/adding air vents/traps where appropriate, examining near boiler piping for the creation of the driest steam possible, and evaluating boiler/radiator/distribution pipe sizing relative to heating loads; listed in increasing order of work required.

    By decreasing the total volume of the system relative to the size of the boiler you very well could be making the system less efficient by oversizing the boiler for the connected loaded.

    With the other radiators shut off your boiler is plowing a greater volume of steam into that radiator that otherwise would be more evenly distributed throughout the system, thereby increasing the density of the steam, which makes it wetter, which leads to more condensation in the radiator, which leads to noises made when the condensate is trying to coexist with steam.