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Frustrated? Just Vent!


This is a post boiler one pipe steam installation conundrum. My new boiler install required drip legs on each of the two mains since they both are partially counterflow. Ten days ago I had a 1” drip installed on the longer of the two 2” counterflow mains which runs for 26’ before turning parallel. It feeds the front of the house and the rads on that mains keep venting even after the main vents have closed and continue to vent for over 20 mins till the boiler shuts off on temp. All the rads on this circuit are partially hot.

However, if I increase the stat for a 2 degree temp rise, the boiler runs longer, all the rads in the front heat up uniformly and the vents on them close.

I had Gorton C, 4, and 5s on the rads and I have replaced them with new Heat Timer vents, fully open, to see if the rads will close sooner. They don’t, but they heat up faster and the boiler shuts off 7-8 mins sooner. I have a Big Mouth and a B@G Varivent at the end of the mains on an 3/4” antler. I have checked that they shut off completely after venting for 15 mins on a warm start.

How do I vent this mains and the rads faster so that they heat up at about the same rate as they did with the old boiler?

Thanks for your assistance in advance


  • Steamhead
    Steamhead Member Posts: 16,844
    What is the length and diameter of each of your steam mains?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • PhilKulkarni
    PhilKulkarni Member Posts: 70
    Dimensions of mains-

    Front of the house:

    2”X25.5’ counterflow, dripped
    2”x13’ parallel flow with 3 risers
    1 1/4”X22.5’ parallel flow till the main vents where it turns into a wet return


    1 1/4”X1.5’ first floor, feeding the largest radiator. Has a 5” runout.
    1 1/4”X10.2’ second floor. Has a 4” runout.
    1/2”X10.2’ second floor. Connected directly to an angle valve.
    1 1/2”X19.3” third floor. Has a 4” runout. Based on the location of this rad and the riser in the crawl space, it is likely that this riser has 6-7’ of 1 1/4” runout inside the walls.

    All rads on this loop have HeatTimer Varivents fully open.

    Back of the house:

    2”X14’ counterflow, not currently dripped
    2”X8.5’ of parallel flow ending in a wet return. The main vents are 10” before the 90 elbow.

    There are Two 2” risers on the parallel sections feeding three floors. one of them is split with a tee and has 3/4” horizontal runs of 4’ and 5’ and then vertical into the walls for 10-12” before each connects to a rad on the first floor. The runouts appear to be pitched correctly. There is no hammer.

    The other 2” riser has a 3’ runout before disappearing into the back wall. One of the rads on the second floor is directly on top of it, thus the riser ht is 1 1/4”x 10.2’. There is a smaller rad in the second floor bathroom also fed from this riser but that has a 3/4” pipe. I suspect there is at least a 6’ runout in the wall to this rad.This rad heats up fast but makes a gurgling sound.

    There is one rad on the third floor so that riser is at least 1 1/4”X19.3’ with perhaps a 2’ runout. The other is a small rad in the bathroom also on a 3/4” riser. I suspect there is at least a 6’ runout to this rad. This rad heats fast with no gurgling sound.

    All the rads on this loop have Ventrites that I have adjusted to heat them at the same rate as possible.
  • PhilKulkarni
    PhilKulkarni Member Posts: 70
    Hello everyone,

    My boiler operates at 0.5psi; almost zero while the main vents are still open. The Big Mouths expel air 2.5CFM at a manifold pressure of 2 oz. I can't find the venting capacity of the B&G VariVent. I am thinking the Big Mouth and the VariVent at the end of the longer mains are grossly inadequate since the pressure at their inlets due to the long mains is probably close to zero.

    Will it help to insert another tee and install another vent at the end of the 2" main where it is reduced to a 1 1/4" dry return? Will that speed up the venting since the pressure gradient there would be higher? I was thinking of 2XGorton #2. Then beyond these vents, there would be approx 21' of the 1 1/4" pipe before the steam reaches the present vents you see in the pic.

    Your guidance would be appreciated.