Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit

sizing main vents

frank_45 Member Posts: 3
In preparation for the upcoming heating season, one of the jobs I’m looking at is checking if my main vents are adequately sized. Going through my copy of G. Gill & S. Pajek's “Balancing Steam Systems”, a question arose regarding their Noel Method.

They describe removing the main vent and timing how long it takes the end of the main to get hot with the open pipe. When you have multiple mains (in my case 4), should all vents be removed simultaneously and each main timed or should they be timed removing 1 vent at a time?


  • gerry gill
    gerry gill Member Posts: 3,010
    you could do it either way,

    but if you do all four at once, you may get steam to one first, so you have to be prepared for that..if doing all four at once i would put full port ball valves on each temporarily so that when the steam gets to one first, you can then note its time, and close the valve simulating the steam closing the air vent, then find the next one to get may want a helper with you if you try all four at once..

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
    Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.

  • frank_45
    frank_45 Member Posts: 3
    mian vents

    Thanks. I like the idea of the ball valves on each of the 4 mains.
  • Mike Cascio
    Mike Cascio Member Posts: 140

    I thought heavily on the subject on sizing vents for radiators and vents and thought of a way that would be a little bit more accurate in sizing vents.

    Based on the principle that the dead men used for piping radiator runouts which is stretching out the run (Fittings, And Valves) into equivalent feet of pipe run. They would then pipe out every run to have the same equivalent feet of pipe run and every radiator would heat up the same. Now obviously many of the dead men did not do this se we are plauged with uneven heating. I figured that if we reverse the process into the sizing of air vents everything can heat very evenly.

    Lets say there is a main with 2 inch pipe. On this main there are 3 elbows and 4 tees. The actual pipe length is 35 feet. Then the elbows would equal (off the top of my head) 3*3=9 feet and the tees would be 7*4=28 feet 9+28+35 = 73 feet. 73 feet times the cfm per foot of the pipe would give us a certain number. This number would then be examined on the chart for the appropriate venting rate. Obviously with radiators, you would then size upon how many minutes you want for the radiator to heat up.

    I used this system when resizing the main vents and radiator vents on my Grandmothers system and it works very well. The Steam gets to the radiators exactly when you want them to which makes it very even.

    Take care,

    Michael J. Cascio
  • Mike Cascio
    Mike Cascio Member Posts: 140

This discussion has been closed.