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Steam in returns

Paul3 Member Posts: 14
Firstly, thanks to all the folks that contribute to this forum. As a homeowner with an older steam system, I find it very helpful.

Basically I am trying to figure out how steam is getting into the return lines, causing banging in return at one two-pipe radiator. Evidence of this is return on the second floor registering over 200 degrees, and returns in the basement, below the “theoretical” false water line registering 200 degrees. Banging is on the return side of the problem radiator.

This issue may have been going on a while, but stuck at home during the past year, I’ve had time to do further investigation.

Info on the system:
  • Single family home north of Boston
  • Early 1900 steam system with a combination of one pipe and two pipe radiators.
  • System heats well and quietly with the exception above.
  • Weil McLain boiler, recently installed, no change in piping, working well.
  • Using a Vaporstat, cut out at 12 oz and cut in at 4 oz
  • No traps on any radiators… installed this way about 100 years ago. All radiators and main vents relatively new (2-4 years old)
  • False water line measured with a laser level, is 6 inches above the point where main drip and radiator return meet in the basement. See diagram.
  • I’ve opened the upstairs floors and have a really good idea of the piping near the problem radiator. I can confirm that where the supply enters the second floor its gets up to 200 degrees very quickly. A few minutes later, the return running beside the supply also gets to about 200 degrees. Even with the supply on the radiator closed, the return side still gets up to 200 degrees. There are no other radiators on this part of the system.
  • Diagram and picture of inverted U below

    • Is it possible the water in the returns is NOT actually at the FWL level?
    • Could the water in the FWL be moving up and down?
    • Is the FWL piping correct?
    • Should I just have the drip-to-return connection moved closer to the floor? The boiler water level is about 28" from the floor

      Any suggestions would be greatly appreciated!


    EBEBRATT-Ed Member Posts: 10,290
    edited April 9
    The only thing I can think of is to lower the tee on the return line that the supply tee drips into. Not sure if that is the complete fix though.

    If that tee is submerged under water no steam can get back into the return. You need to find out where the steam is getting into that return
  • dopey27177
    dopey27177 Member Posts: 748
    1. The false water line is to high. lower the false water line to slightly above the steam chest of the boiler. that is about 2 inches below the boiler jacket.
    2. Lower the drip from the steam supply to the second floor radiator to the main return on the floor. The return line from the second floor radiator returns a very small mount of condensate to the main return which leaves an open line for steam from the drip to work its way into the return from the second floor radiator causing the banging.
  • Jamie Hall
    Jamie Hall Member Posts: 17,080
    If that false water line is not equalized -- and I don't see any equalizer on it either in the photo or in the diagram, it's not a false water line -- it's just a siphon. You need an equalizer on that, tied tied into the system side -- not the boiler side.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Steamhead
    Steamhead Member Posts: 14,840
    I'm not sure the FWL is the problem. Some questions:

    1- is there an air vent on that 2nd floor radiator?

    2- when the return from the 2nd floor radiator starts getting hot, does it start from the radiator end or the drip end?
    All Steamed Up, Inc.
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Paul3
    Paul3 Member Posts: 14
    Thanks for the reply. To your questions:
    • Yes, there is a vent on the 2nd floor radiator, relatively new and does allow air to escape
    • Yes, the radiator gets hot from the drip/return end. I have closed the supply/steam valve and still the return side gets very hot (200 degrees measured with an IR thermometer) with the return valve open. Both supply and return valves are new and I am pretty sure close completely.

      As a further test, I opened the nearby closet floor where the steam/supply and return pipes come up from the cellar and then run along under the second floor to the radiator. At this spot, both the steam/supply and return side get up 200 degrees... first on the supply side and then a few minutes later on the return side.

      Hope this helps, and thanks again for all your advice!
  • Jamie Hall
    Jamie Hall Member Posts: 17,080
    The plot thickens. There is a vent on that radiator? And there are valves on both the supply line and on the return line? And the system is early 1900s?

    Why am I thinking this may be a two pipe air vent system, and not a later conventional system?

    In which case the problem is really very different. It may not be why is steam getting into the return line, but where is condensate allowed to collect in the return line so it can't drain freely to the boiler. Since that inverted U isn't equalized, it's not a false water line at all, and steam pressure in the main may quite happily lower the water level in the system side enough to allow steam to pass between the drip and the return line -- a matter of only 6 inches, according to the diagram.

    I'll have to sit and think about the dynamics of this arrangement, but possible places for trouble are in that connection or in the top of that inverted U.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • mattmia2
    mattmia2 Member Posts: 3,972
    Do the other radiators have a vent?
  • Paul3
    Paul3 Member Posts: 14
    Yes, a thick plot it is... Some quick replies to your questions
    • The house was built in 1887, and we think the initial steam system installed in about 1900, given that some second floor pipes are run in chases, not in walls.
    • There is a mix of one pipe and two pipe radiators. All radiators have vents. All heat up nicely.
    • On all the two pipe radiators there is a valve on both the supply and return side.
    • While the banging is only bad in one radiator, I did check the other two pipe radiators, and the returns on these also get quite hot very quickly after start up.
    • More detail than you might want... about 18 years ago I had a new boiler installed. At that time they installed "inverted U" which was about 6 feet high (I never learned why). This caused all kinds of problems, mostly terrible banging and water spurting out of the mains. The A dimension (top of the U to the lowest point on the steam mains) was about 4 inches. After much discussion, the plumber to lower the inverted U to the current height (45"), and things got much better. I always assumed this was a false water line... the plumber passed away and I cannot find out what he was thinking.
    • And if you are wondering, yes, the boiler only lasted 18 years (replaced last month). I had all kinds of leaks in returns over the years forcing me to add water more than I should have. Now all the returns in the cellar are new, and all the radiator valves new or repacked (i.e. not leaking). Good lessons learned!
    I really appreciate the feedback. Other ideas on things to check would be great. That said, I don't want to take up too much of your time. Thanks!
  • gerry gill
    gerry gill Member Posts: 3,010
    If you only have 6” difference in submerged tee distance, that’s about 4 ounces of pressure if I did my math right. After that, in my minds eye, I see steam blowing thru the connection like a fart in a bathtub. And as Jamie said, fix the false water line.
    Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.

  • Jamie Hall
    Jamie Hall Member Posts: 17,080
    Inelegant there, @gerry gill , but quite exact! More and more I think that this was -- and should be -- a two pipe air vent system. So... seems to me here are really two choices. Fix that U tube thingy so it really is a false water line -- or take it out altogether and find any other places which got "improved". The former is probably a slightly more conservative approach, but the latter is what I'd personally prefer to do. It would help if you had a contractor to assist who really knew steam, however. Where are you located? We just may know someone who's qualified.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • dopey27177
    dopey27177 Member Posts: 748
    look at the drip from the stem line to the second floor radiator.
    If you are at 1 psi steam pressure the steam pressure can push through the 6" water column and enter the return line from the second floor radiator.
    1 PSI steam can raise the water column 2.3 feet. Because very little condensate enters the drip from the second floor radiator steam can enter the return line and rise up the return because the radiator vent vents any air in the return line and the result will be banging in the radiator and return line.

    Lower the drip line to the floor or to the 28" level from the floor.

  • clammy
    clammy Member Posts: 2,668
    As others have said it looks like that false water line does not have a equalizer line piped to it which make it functionality quite iffy at best plus you would need to be running lower pressure then what your set at from prevent it from hammering especially giving it’s height . I would say if all the drips out in the system are tied into the wet returns below the water level the fwl may not be needed if your running lower pressures and have a16 water seal you should be safe at 8 oz . Also I would have to agree w Gerry and jake about lowering that drip down into the wet return to help prevent steam from passing up that drip . Brake out that later level and do some detective work. Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • Paul3
    Paul3 Member Posts: 14
    Folks, thanks for the time and education. Based on your comments, I will have the problem radiator drip lowered to below 28". I should be able to get it to about 8" to 12" off the floor (in other words 16" to 20" below the boiler water level). As the returns in the floor are all new, this should be pretty easy to do. Based on the outcome, I will likely have the same thing done in two other similar spots and will dig deeper into the Inverted U.

    I will reduce cut out from current 12 oz to 10 oz to test as well.

    As for location, I am in Danvers MA, about 20 miles north of Boston. Recommendations on a steam expert who could check out the site would be appreciated.

    Also, if there are things I can do as a somewhat educated home owner with a steam system to help on this forum let me know. It would be nice to give back.
  • Jamie Hall
    Jamie Hall Member Posts: 17,080
    Ryan at @New England SteamWorks is your man. And I think what you are proposing may just do it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Paul3
    Paul3 Member Posts: 14
    Some follow up. A number of you suggested lowering the drip/return connection. This is what I did - lowered it to about 12" above the floor, which is about 16" below the boiler water line (mid-point in sight tube). The banging is gone, and radiator warms nicely. I did this in another problem spot as well, also with good results. So thank you all!

    Related: during the process I found someone who knew the now-deceased fellow who installed the replacement boiler back in 2002. This fellow was a big believer in "loop seals" which is likely what my "inverted U thingy" is. I cannot really figure out what a "loop seal" is supposed to do. I'm not planning to change anything as the system is running very well now. I ask more of intellectual curiosity, but any thoughts on "loop seals" would be appreciated. Thanks again!
    EBEBRATT-Ed Member Posts: 10,290

    Glad it worked.

    Loop seals are sometimes used in place of traps to keep steam out of the returns. Loop seals are just pipe and fittings, nothing to go wrong unless they plug up. Steam traps are always a maintenance item