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Two steam radiators not heating

Three story eight unit brick building with 500,000 btu gas fired steam boiler Weil McLain with one pipe steam. Main building has annex with two wings..

Radiators in room most removed from main (which is insulated) do not heat until the end of the heating cycle. Branch lines feeding radiators, while insulated pass, through unheated crawl space.Different steam vents on all cold radiators have failed to cure the problem.

the main building heats  well but these two rooms in the wings of the annex do not. Why are they not heating at the appropriate time in the heating cycle?


  • BobC
    BobC Member Posts: 5,473
    edited September 2011

    Venting is a little bit of am art.

    What do you have for vents on the steam mains? You want to vent the steam mains very quickly, how long are the mains and what size pipe? Can you tell if the mains are heating up at a similar rate?

    Check the slope on the main that feeds these two radiators and the pipe leading to the radiators to make sure there is a positive slope to condensing steam can find it's way back to the boiler. If there is a sag in the piping that can cause the steam to condense and pooling water will condense steam and may cause water hammer. See if you can determine haw fast the steam is progressing down the main and piping that feeds those two radiators. If the steam seems to be getting very close to the radiayor inlet the valves may not be fully open even if they appear to be.

    You stated that these were the last two radiators on that steam main, how far are they from the next radiator and does it take longer to heat than most of the other radiators? Are the problem radiators on a higher floor?

    There is a chance that you will have to vent all the radiators slower so that steam can propagate down to the end of the mains. What kind of radiator vents are on all the radiators? Is the heat controlled by a thermostat and is that thermostat near a rasiator that is heating up quickly?

    A rough diagram of the piping wiyj aproximate pipe lengths and sizes would help us see what your dealing with.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
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