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Venting Returns / Mains in 2 Pipe

Have a 30,000 sf building with 10 large apartment units. 1M BTU Smith boiler.  Just removed all one pipe vents at the radiators and installed new steam traps and danfoss valves at every radiator.  Also cleaned up any piping issues leading in and out of individual radiators.  Now working on ensuring the the correct vents are in place on the main feed lines and return lines.  The building has three mains:  Front and Rear to all of the radiators, and a middle that goes to the roof's wood gravity tank and pressure tank for the sprinklers.  Only two returns (roof tank is one-pipe). 

The top floor apartment (one open 5,000 sf space) has been running approximately 8 degrees colder than the rest of the building!  (they also don't have insulation in their ceiling, as they recently exposed the joists for asthetic purposes)

Plan was to install one Gorton #2 on the top floor at end of horizontal run of both the front and steam mains.  Also planning to install one Gorton #2 on each dry return pipe at the ceiling of the basement where the returns begin their horizontal run back towards the basement.  Lastly, was planning to put one more Gorton #2 on a T coming up about 5 feet from the now combined wet return.  Should this just be an open pipe?

Does this plan make sense?  Need more Gortons?  What about just open pipes on the return lines at the basement ceilings?

thanks for any thoughts.


  • Rod
    Rod Posts: 2,067
    Main Vents

    Hi - If the ends of the two pipe steam mains drop into a wet return (no f&t trap)  then you will need main vent(s) there. You will also need a main vent (s)  on the end of the “one pipe” (which I’m assuming is counterflow) to the tank.

    As for the venting the returns, while in theory you could just leave the pipes open, in practice you should install main vents as then in the eventually that if a  trap fails, they prevent steam filling the basement which with a  large boiler could be rather spectacular and would probably result in a panicked call to the fire department. Each return main should drop individually into the wet return and shouldn’t join until they are below the boiler waterline. You will need adequate venting just before the return pipe drops into the wet return.

    I’m not sure quite what you are attempting to do in the 5000 sq ft. apt. with the bare joists. It maybe that the EDR of the installed radiators just can’t keep up with the heat loss as a result of the removed insulation. The obvious solution here is to retrofit some sort new insulation or to add more radiation.

    As to the Main Vents -My general feeling is that even with strategically placed single Gorton #2s  may not be enough venting for so large a system. You might want to get a very good downloadable book, ”Balancing Steam Systems...” by Gerry Gill and Steve Pajek, It’s available on this website in the “Shop” section at the top of the page. Here is a direct link to the book: http://www.heatinghelp.com/products/Books/5/146/Balancing-Steam-Systems-Using-a-Vent-Capacity-Chart-by-Gerry-Gill-and-Steve-Pajek

    It has great charts on venting and shows how to calculate the venting needs of your steam system.

    You might also want to take a look at Gerry Gill’s website as he has a lot of good info on venting and steam heating in general. http://www.gwgillplumbingandheating.com/webapp/GetPage?pid=415

    Be sure to take a look at his article on “Air Locking a Two Pipe Steam System” as this might apply to your system.


    With the TRVs and the new traps it sounds as though you are on your way to having a very satisfactory steam system.

    - Rod
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
    more venting needed

    i have 1,050,000 btu, 55 rads, and 17 gorton #2's on my one pipe steam system.

    there is no such thing in my book as over-venting, or under-pressure [mine is 2 ounces most of the time].--nbc
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