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one-pipe steam system

I have a one pipe steam system, the radiators are not heating evenly, and the two that are located on the outside wall of the addition are cold. another contractor installed the 1 1/4 copper steam main to the addition ( I only installed the new utica steam boiler and insulated the copper pipes)  and he did not pitch the main properly and added no main steam vents. The lines going to the cast iron heaters

are pitched under the addition in the crawl space. Two of the four heaters that do get hot to the touch, their air bleeders are hissing air.  Is the lack of a Gorton air vent in the main the problem or is the condensate laying in the pipe causing the steam not travel to the 2 heaters.  I have your book, pocket full of steam problems, but wanted to see if this is a condition out of the ordinary.

p.s. the main line is pitched from the boiler header to the addition, but not under the addition, the main is 17 feet long, ?? do I need more than 1 vent

I just insulated all the 1 1/4 pipes yesterday, but didn't seem to help much.


  • Unknown
    edited February 2010
    1 pipe steam addition

    Let's start with the original steam system. How many radiators are attached the original main?  Is there only one steam main on the original system? You mentioned the "the main line is pitched from the boiler header to the addition" - What is the size of the original steam main - Length and pipe size?  Are there main vents on the original main? Since it "slopes away from the boiler there should be a return line to the boiler -what size is this?

    New addition-  There are 4 radiators in the new addition? Two of these radiators aren't getting hot? Are the two radiators that aren't getting hot, the farthest from the boiler?

    How long is the new steam main under the addition? Does it have a return pipe?

    You mentioned the steam line under the addition isn't pitched. All steam lines must have pitch. Steam lines carry both steam and condensate (water) and while steam, being a gas, can travel in all directions, condensate is a liquid and needs slope (pitch) to flow back to the boiler.  You need to get the mains straightened out and add some main venting as a start.

    If you could provide some pictures of where the new main is attached to the old main that might be a help too. I've attached a picture of a typical parallel flow system which sounds ( "flows away from the boiler") your original system which might be of help to you.

    - Rod
  • Jamie Hall
    Jamie Hall Member Posts: 18,689
    I'll go a little farther out on a limb

    than Rod, and make the assumption -- since you mention hissing "air bleeders", that you are talking about hissing vents on the radiators, and that this is one pipe steam.

    The fundamental question with regard to the lines in the addition, then, there are two questions.  First, you mention that the main line pitches from the boiler to the addition.  How does the condensate in that line get back to the boiler?  Is there a drip at the end of that section?  There should be... then, if there is, the question is how does the condensate in the line under the addition get back to the boiler?  It must pitch either towards the boiler (the connection with the main) or away.  It can't just sit there level.  If it pitches away, you can treat it (and size it) as a continuation of the main.  Put a vent at the end of it, and a drip or wet return (pitched towards the boiler!!) from the end of it.  However, you could also size it as a horizontal runout, pitched back towards the main, in which case it is a counterflow runout, and needs to be pitched at at least a half inch per foot back to the main -- and has limited capacity.

    So we really need a little more information, but the above comments should help as a start.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • krtuck
    krtuck Member Posts: 3
    1 pipe steam system


    based on your comments, there is no wet condensate return line back to the boiler from the 4 cast heaters which heat the addition on the house. Its basically setup as one 1 1/4" copper pipe to all 4 heaters.. and there are no vents on the main. and no pitch or 1" for 20 feet. As the copper pipe enters the foundation of the addition, it stops pitching the rest of the 17 or 18 feet run. the pipe however from the near boiler piping header is pitched to this point.

    The main is 2" black iron pipe, and the rest of the 2 story house is a single pipe system. I think the plumbing contractor (before I stepped into this mess) didn't provide a means to get the condensate back to the boiler wet condensate return. This system has a wet (1") and a dry (1 1/4") condensate return lines....

    Rod:  Yes, the 2 coldest heaters are the furthest from the boiler, along the outside wall of the house ( in between a 6 foot walk out french door), and there is no return pipe and no vents, and the main is about 18 feet long ( 1 1/4 copper)... So based on your schematic diagram, this addition must have a return wet condensate line, which based on what I am finding in Dan's books is correct????....  thanks for the Help and info.  You would be surprised how many wholesalers here on the island know jack about steam or associated issues with steam....

    Thanks Guys,    Chuck
  • Steam System

    Hi Chuck - Thanks for the info on your system.  A couple more questions: What island do you live on and you mentioned "Dan's books", which books do you have? I'm hoping "The Lost Art of Steam Heating" as we can then refer you to a specific page in it.

    On the addition you don't have to have a return line as you could run it as a counterflow main

    but you will need pitch of 1 inch in 10 feet. (Page 83-84 -"The Lost Art..")  A counter flow main

    would slope upward from the end of the old main. The steam would travel "uphill" and the condensate (water) would flow back down the new main and into the dry return of the old main and then back to the boiler. You'd need a vent at the very top (high) end of the counterflow main   (just past where the last radiator lateral is attached )  You would probably also need a main vent near the end of your old 2 inch main also.

    - Rod
  • krtuck
    krtuck Member Posts: 3
    one pipe steam

    Thanks for the return email.  I am working a job for one of my customers on long island NY, I have the book, pocket full of steam problems but not Dan's other book that your referring too, I need to purchase it this week...I'll soon have other steam boiler installs near by to heamstead, NY....  

    So what your saying is I need an independent 1 1/4" run back to the dry return of the boiler ( hartford loop ) ....thanks, and I understand about the air vent, I printed out a schematic of that on the internet.....

    Thanks for the tech, tip,   my email is [email protected]
  • Check email

    Hi Chuck - I emailed you a diagram

    - Rod
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