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Increasing Main Venting

I’m trying to figure out if I have enough main venting and need a little help. I’m not great with math and don’t know how to calculate venting rates and main capacities. I have 3, 2” mains...62ft main has 2 big mouths, 50ft main has 1 big mouth, 20ft main has 2 Gorton 1’s. 
Is there enough venting on these mains? If it’s not, what would you add to any of these mains? 


  • Jamie Hall
    Jamie Hall Member Posts: 22,969
    Should be more than enough -- and math isn't your friend. If you have a low pressure gauge on the boiler, it's easy: fire the boiler cold. As soon as it starts to steam, keep an eye on the gauge. As steam is filling the mains -- and before it gets to even the closest radiator -- the gauge should rise; depending on the length of the mains, usually to somewhere between 1 and 4 ounces, though usually at the low end. Then -- and this is important -- it should just sit there more or less constant until most of the radiators are close to full, when it will start to rise again as their vents or traps (as the case may be) close. If it does that, you have enough main venting. If it doesn't -- if the pressure continues to rise steadily, you don't.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England