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Main Venting Review

Fred Member Posts: 8,542
I have a 112 year old home with a Burnham boiler and one pipe steam system. The boiler is 30 years old and virtually all of the piping is original and in great shape. I had to replace a leaking wet return a few years ago. My question/concern is: I have two mains, one branches off in two directions and has two Hoffman #75 vents at one end, just above where it drops into a wet return, and two additional Hoffman 75 vents at the other end, about 4 feet before it makes a 90 degree turn and returns to the boiler/wet return.

The second main takes off in another direction and branches off to a leg that has three radiator risers attached to it.It has a dry return on the end of that leg and runs back to a wet return (no venting). The main then makes a loop and ties back into a common return as main #1 but that  connection is 5 feet down stream (closer to the boiler than the vents at that end of main #1. This all looks like the original setup (except for the Hoffman vents which I replaced and added another one at each end). I have been over the second loop with a fine tooth comb and see no indication that there was ever a vent on that loop.The system is very quiet, runs great, radiators all get hot within a minute or two of each other and I'm running at between .5psi to 1psi except on really cold days (zero or below)when my boiler may cut out on pressure a couple times.

Have any of the pros on this site seen this type layout and should I be concerned about adding vents to the second main or is it actually pushing air out of the vents on Main #1 near the common return to the boiler? I know they say "If its not broke, don't fix it" but if I can get a little more efficient, maybe I should try. I have a diagram of the layout but I don't know how to post it??


  • Main venting?

    This is one of those situations where a 0-3 psi gauge would tell you how much back-pressure is developed during the initial venting phase. On my 55 rad system, the air escapes at 2 ounces.

    I believe that putting a main vent on the 2nd main has got to be an improvement; however I can't explain the closeness of time of steam radiators between the vented and unvented mains.--NBC
  • Fred
    Fred Member Posts: 8,542
    I know

    I am going to put a 0-3 pressure gauge on the boiler. I ordered one a few days ago but may wait until we have a break in the weather to put it on. The only thing I can figure is that the steam is pushing the air ahead of it and into the common return that goes back to the boiler. That main is 2.5'' pipe. the loop in total is 35 feet to get to the common return. The common return is also 2.5" pipe and is about 40 feet from where this loop connects back to the boiler wet return. In theory their may be enough space in the return pipe to handle the volume??? Does that seem logical?