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Main Vents necessary?

This house has one-pipe counterflow steam. It has kind of an unusual (from the standard description of steam pipes) arrangement. Rather than one main from which all the radiators rise, it basically has four mains. That is, three feet from the boiler the main splits in two, toward the front and the back. Then, 10 to 20 feet further, each branch branches again into two basically equal branches--one goes 20 feet forward to the front of the house, the other 20 feet sideways to the dining room. And the main going backward, after 10 or 20 feet it too branches, one goes another 15 or 20 feet to the back of the house, one goes 20 feet sideways to the kitchen.

In other words, depending on how you count, there are either four mains, or one very short main and four very long "risers." The steam arrives at the radiators at about the same time, and the heat in the house is pretty well balanced right now.

There are no main vents--the only venting comes from the radiators. My question is, is it worth while to install main vents? If I did, what should I do--install four main vents at the ends of the four branches? This should save some money, by allowing the steam to get closer to the radiators faster, but would it make enough of a difference to justify the work and expense?

Thank you!



  • mattmia2
    mattmia2 Member Posts: 9,622
    Not necessary but beneficial. You would put them near the end of the 4 branches.

    How long does it take from when the boiler starts steaming to when the radiators get hot at the vent?
  • dabrakeman
    dabrakeman Member Posts: 551
    Just a fellow homeowner here but I think in your case 4 would be better than 2 and 2 would be better than zero. I know you say you are balanced now which is fine but if you can get the steam through the main branches more quickly I think you will see some improvement in efficiency (steam to the radiators more quickly each cycle).

    What is your accessibility at either the 4 mentioned ends or at the first splits (10-20ft from the boiler)? How is your condensate returned to the boiler, main extensions above the waterline or wet returns below waterline?

    Pictures always help.
  • jhewings
    jhewings Member Posts: 139
    edited November 2022
  • greg556
    greg556 Member Posts: 19
    The piping is fine. My question is about whether installing four main vents at the end of the four mains will improve efficiency enough to justify doing it (the speed of the steam getting to the radiators). Currently it takes around 4 minutes for the steam to reach the farthest radiators. But I know everyone loves pictures, so here are a couple. It's like asking to see pictures of your baby. :)

    The first one shows the risers to the header and the equalizer.

    The second one shows the take off to the main. The near side is the condensate return.

    The third one shows where that pipe was connected to the existing main pipe. That is the one that goes out three feet then branches left and right (toward the front and rear of the house). (I just noticed you can actually see that T at the end of the main pipe in this picture.)

  • Jamie Hall
    Jamie Hall Member Posts: 23,272
    If it really only takes four minutes for the steam to go from the header to the farthest radiator... the best place to put your time and money is in insulating every pipe you can get at which carries steam.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • dabrakeman
    dabrakeman Member Posts: 551
    I guess theoretically if you were able to shorten your cycles say by 1 minute each cycle then for a 250000btu/hr input boiler assuming 16 cycles per day or 480 cycles per month that could be almost 2Mcf gas saved per month. Over 4 heating months say 8Mcf and if gas goes up to say $8/Mcf that could be about $64 per heating season. If shave 2minutes off then double that.
  • greg556
    greg556 Member Posts: 19
    Thank you for your help, everyone!