Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Some questions about replacing part of a steam main

baj702 Member Posts: 43

This is a 4 story apartment building. 1 basement level and then 3 floors above that. The boiler is in the basement. The steam main goes into a pit and the pit is about 6 feet deep where there is a condensate tank. There are tunnels (about 3 or 4 feet high below the basement level) that follow the steam main.

I need to replace the steam main from the green dot back to the condensate tank. This is about 60 feet. At the green dot the main reduces from 4 inches to 3 inches (so replace everything starting after that reducer). 12 feet past that there is a 1-1/2 riser as shown in the picture. I think it feeds 8 small radiators of about 9 EDR each or 72 EDR total. There is another 1-1/2 riser near the end, but the radiators on that riser have been taken out. The main reduces after each riser but doesn't go below 1-1/4 until in the pit just before the condensate tank where it reduces to 1", goes through a strainer, reduces to 3/4 and goes through the F&T trap and then into the condensate tank. There is also the condensate return line that comes into the condensate tank. I think it's 1-1/2 inches

My plan was to immediately reduce to 2 inches until I get to the 1-1/2 riser. Then reduce to 1-1/2 until I'm about 10' from the condensate tank, and then 1-1/4.

The F&T trap is in the pit just before the condensate tank. There doesn't seem to be any vents.

Can I do this?

Also, in the picture there is a 1-1/2 riser, a 3/4 line that feeds a radiator, but I don't know what that other pipe is with a 90 and a plug? This is a two pipe system, the condensate return line isn't shown in the picture, but it's there.


  • Jamie Hall
    Jamie Hall Member Posts: 21,573
    I'll let others comment on the line size -- though I suspect what you are proposing would work -- but ... no vents? I presume the condensate tank is vented, which vents the wet return, but... no other vents? You say it's a two pipe system -- if so, I rather think it will be a lot quicker and more even if you get some vents on both the steam main and on the dry return.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EBEBRATT-Ed Member Posts: 13,851
    Before you do any reducing I would calculate the edr of all the radiation you plan on keeping operational and then size the pipe accordingly. Make sure that what you remove stays removed. Everybody always want's to install 2" and under. It always becomes "big enough" when the tools an knowhow to install 2 1/2 and up aren't available...Dosent make it right though

    If you have a trap in the main return it's probably a "master trap" that was added as a band aid. The system will never work right until you remove it and fix the remaining traps.
  • baj702
    baj702 Member Posts: 43

    I should clarify, there is a return line that goes around the perimeter of the building like the main (red line in the floor plan view). They meet after the F&T trap on the main literally 12 inches before the condensate tank. So, if what separates the main from the return is the F&T trap, the steam main is a steam main all the way to the condensate tank minus about 2 feet.
    EBEBRATT-Ed Member Posts: 13,851
    If the trap is dripping the end of the steam main into the return then it is probably ok