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2 pipe "missing link" system???

NewSteamer Member Posts: 2
edited November 2020 in Strictly Steam

I recently moved into a new home with steam heat, and not only is it my first steam system but it also appears to be a rare one based on what little I have been able to find already.

Here are the details:
- All of my radiators have 2 pipes
- Both pipes are on the bottom of the radiators (one on each side)
- Both pipes have an open/close valve
- One pipe is always slightly smaller than the other
- All of my radiators have an adjustable vent (a few different types, but all are adjustable)
- I have 2 different styles of radiator. Two rads are short but wide and have the typical accordion look and all the rest are taller and have a double wide row of vertical pipes

My actual problem/s:
- I need to work on balancing the system, but want to make sure I should approach it like a 1-pipe system (new vents and slow adjustments?)
- I am getting water hammer from only the 2 accordion type rads mentioned above, not sure where to start

PS: The home was not used in the winter for the last 10 years so not much attention was given to balancing and noise

Any help is much appreciated!


  • Jamie Hall
    Jamie Hall Member Posts: 22,912
    That's an uncommon, but not new system -- two pipe air vent system. They were a transition between one pipe steam, which came first, and the more modern two pipe systems which have separate steam mains and returns, and some means to prevent steam from getting through the radiators to the returns -- traps, orifices, calibrated valves...

    That said, it behaves, for most purposes, like a one pipe steam system, and balancing the system is done exactly like a one pipe system. Make sure, first, that there is adequate venting on the mains themselves. Once that is done, one can balance it -- patiently -- by putting slower vents on radiators which heat too fast (putting faster vents on slow radiators doesn't usually work all that well, until there's nothing else to be done). Do this patiently, and try not to change too many things at once, since they all interact with each other.

    The banging -- assuming it is water hammer, which is quite likely -- is approached in the usual way: try to identify any horizontal or near horizontal pipes feeding those radiators, and make sure that they can drain back to the main. You have to check both pipes from the radiator!

    Also, like a one pipe system, make that the valves -- at both ends of the radiators -- are fully open.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • NewSteamer
    NewSteamer Member Posts: 2
    Thanks Jamie. The house was built in 1894 so I was pretty sure my 2-pipe steam was really a one pipe system with 2 pipes :)

    Now I have to look up what venting looks like on the mains, I'm not sure I've seen anything like that in my basement. Will also check the pitch of the pipes.

    Is there any chance the system needs to be flushed of scale/buildup? I've never done that on steam but I think it's a thing?
  • Jamie Hall
    Jamie Hall Member Posts: 22,912
    There is sometimes a need to flush wet returns -- pipes below the boiler water line. It is almost unheard of for anything to build up in pipes -- returns or mains -- above the water line. So... no, except possibly if you do have some wet returns (on the whole, though probably not...)
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England