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Main air line vent sizing and operation

Hello friends!

I got some great advice from you helpful chaps before and I am hoping you will come through again. I have a picture of my two mail line vents. One works, one doesnt. I obviously need to replace the other as it does not work and for the 20 minutes or less that the heat will cycle on the radiator vents really never stop hissing. I assume this to be because of not enough air leaving the system and it is being forced out the radiator vents. This is when the whole system is warm and I would assume the radiator vents would shut down the flow as they are too hot to touch. They are not stuck open as we have washed and checked each one and they all hiss during operation. So I have the following questions:

1. Are the 2 #35 vent rite vents sized right for my system?
2. Is my assumption about why the radiator vents hiss for so long correct?
3. Any helpful comments are welcomed.


  • BobC
    BobC Member Posts: 5,471
    The number 35 vents have low cfm ratings, you probably need at least a Gorto / maid o mist #1 and may need a B&J Bigmouth.
    It depents on how long the mains are and what diameter the pipe is.

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