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Thread: steam main vent

  1. #1
    Join Date
    Nov 2008
    Posts
    1

    Post steam main vent

    my dads home built in 1930 or so is a three 3 family home with two apartments upstairs and first floor is a single apartment where they reside and also have half finished basement with bedroom. one of the two tenants upstairs complained that it was not that warm last winter now that this winter is almost upon us i was looking into possible causes of this condition. ive noticed that the vent on the main in the basement is spitting brown water and vapor and was wondering if that could be the cause of the radiators not really gettiing at full temperature thus not warming that apartment fully.(its a single pipe steam system) or could it be the radiator vents.also no isulation on steam mains in basement..its seemed ok to me when i was up there but i like the cold weather so im not a good judge. im probably going to change the vent anyway. also on first floor they have two radiators turned off because it gets too warm,it was renovated so i just think its well insulated.my mom raises thermostat to 78 degrees or more sometimes , im thinking thats a little too high

  2. #2
    Join Date
    Feb 2008
    Posts
    550

    Default Re: steam main vent

    It sounds like the problem areas of the steam system need a little TLC.

    If you want to do the work yourself, figure on doing a lot of "troubleshooting" (detective work) before you can pinpoint the exact cause of the problem.

    Steam systems have the disadvantage of throwing a lot of dirty water/rust paticles as the boiler does it's job of heating---the pipes are usually made of steel & thus there is a lot of rust.

    The brown water you see is iron oxide & will eventually clog the piping & shut down the radiators in that branch.

    To review the process---the boiler heats up to 212 degrees & creates steam that moves rapidly thru the main pipes to the rads.

    Since there is already air in the piping, this has to be expelled ahead of the steam thru the air vent.

    Once the hot steam hits the little metal alcohol-filled bellows inside the main air vent, it should expand & close the vent opening to allow the steam to continue up to the branch rads.

    Air is again pushed ahead of the steam, & the same process is repeated at the rad---the air is pushed out, the hot steam hits the rad vent bellows & closes the vent to let the steam heat the rad.

    Once the steam cools it turns back into water (condensate) & has to be allowed by gravity to find its way back to the boiler to be reheated.

    Any dirt paticles in the bellows needle valves will cause steam to escape & waste heat--any clogged pipes, or pipes not slightly pitched back toward the boiler will not allow water flow back to the boiler & block steam from getting to the rads---water-blocked piping can also cause "water hammer" or loud pipe banging.

    Buy a scew-on metal plug that will fit into the problematic main so you can test the main vent & the piping leading to the branch rads--- or simply shut down the boiler (on/off switch) for an hour or two during the warm part of the day.

    Clean the main vent by soaking it in vinegar & clean any crud present in the needle valve area.

    Blow thru the vent--it should pass air freely---heat the vent in a pan of boiling water for a minute or two & then using heavy gloves, & a plastic tube to the vent, blow air thru it again---the hot vent should be closed & not let air thru--buy a new one if it fails this test.

    While the vent is off, make sure the adjacent piping is clear of rust crud & water flows freely thru it---check the pitch of all the piping with a torpedo level to make sure the pipes pitch slightly back to allow the water condensate to return to the boiler.

    Check the air vent at the rad in the same way---when the system is heating up, you should first hear air escaping from the rad, then hear it stop when the expanding bellows/needle valve kicks in, then feel the steam heat up the rad.

    There is always the option of deciding to have your heating tech do this work, which may cost several 100$.


    http://www.heatinghelp.com/steam_problems.cfm
    http://www.heatinghelp.com/steam_radiatorsnotheat.cfm
    http://www.heatinghelp.com/newsletter.cfm?id=165
    http://www.oldhousejournal.com/Care_.../magazine/1016
    Last edited by NashuaTech; 11-23-2008 at 12:13 PM.

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