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Loud hiss from vent in return line?

I've got a two-line steam heat system in my house (built ~ 1928); have replaced the boiler and recently insulated all of the steam lines (not the returns). Believe it to be a "Baker" vacuum steam system.

When the thermostat calls for heat, we initially get hammering noises which subside after a little bit, but a vent (replaced about four years ago) on one of the return lines hisses very loudly (no water coming from it that I've noticed) until the thermostat stops calling for heat. Some radiators provide a lot of heat, others to a lesser extent, and a few are always cold.

The system does not, as far as I know, have an F&T trap; each radiator has its own trap (bi-metallic?), and I haven't noticed any hissing at the radiators. The system does have a large elevated cast-iron cylinder (about 18" high and 12" in diameter with a float glass near the boiler, which I think creates the vacuum for the steam mains.

I'm not sure if this is due to a clogged return, or poor return pitching due to house settling, or a poorly-sized vent (or if the vent is making it too easy for steam to escape without going through the radiators) or something else. Also not sure if this is causing the uneven heating across the radiators.

Thank you in advance for your thoughts and ideas.


  • Not sure if it's a Baker

    when you say "large elevated cast-iron cylinder (about 18" high and 12" in diameter with a float glass near the boiler" it sounds a lot like a Trane return trap- a pressure-powered pump that forces water back to the boiler if it can't return on its own.

    If it is a "Baker", congratulations on bringing another brand of Vapor heating to our attention. Can you post some pics?

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  • rbwrbw Posts: 2Member
    New information and pix

    I wish I could remember why I think it's called a Baker steam system- maybe one of the first plumbers we hired when we moved in called it that.

    And taking the pictures provided further education- I found a huge amount of steam coming from the vent, with water dripping off the return piping as it condensed. I am convinced that my house has the ability to look at my checkbook and say, "Oh, you still have money? Watch this!"

    I've posted pictures of the furnace room, the elevated cast-iron cylinder, an unknown device on a return line, a photo of the vent and a photo of the old vent (leaning against a return line).

    Seeing the steam coming from the vent (like a mini-sauna) has me concerned; I'd be very grateful for your thoughts.

    Thank you again.
  • Wow!

    That's a new one on me! Not the fact that it's Vapor, but it appears to be a type/brand I haven't seen yet.

    Can't really tell if the cylinder is a Return Trap or a separating chamber for returning water and air. Is there a pipe that connects this unit with the steam main?

    The "unknown device" is a bucket-type trap.

    The old vent is a Gorton #1, and the newer one is a Norca/USAV type that Home Depot still carries.

    Have you found any manufacturer's info on the cylinder, or any radiator valves or traps that look original?

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  • rbwrbw Posts: 2Member
    More pictures

    I tried to take some more pictures of the cylinder; little scary that it seems mysterious! Couldn't find any markings on it, but I know that we replaced the float glass in the front three-four years ago, and it was clear then- it's pretty dirty now, so I guess something is going on in there.

    Looks like the lines at the top of the cylinder go to both the steam mains and an elevated return line, as well as draining at the bottom down to a return line at the level of the bottom of the furnace. Attached a somewhat blurry picture of the top (the thing is in a far corner of the furnace room and pretty hard to get to); not sure if that's helpful.

    Also have attached pictures of a typical radiator, with some detail for the steam valve and the trap. Believe all these are original equipment on the house; the trap is where I think the bi-metallic disks were installed.

    Hope this helps; I am cringing every time I hear the hissing from the vent.

    Thank you again for your time, and for sharing your thoughts.

    PS- Noticed you are in Towson- my wife grew up in Timonium, off York Road.
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