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Looking for confirmation on main vent sizing (check my math)
So I have two mains, each with a Ventrite 35. My suspicions is that that are both undersized and due for replacement, based on comments in this forum and the fact that many of my radiator vents seem under strain, especially those served by the longer of the two mains. So I'm planning to replace them.
I've mapped out the mains my basement, meaning each main/return loop.
Main #1: 25 ft of NPS 2 pipe, with about 20 ft of NPS 1 1/4 return. I've calculated this to be about .775 cubic feet of air, based on the chart in Greening Steam.
Main #2: 15 ft of NPS 2 pipe, with about 15 ft of NPS 1 return. I've guesstimated this to be .43 cubic feet or less, as I'm not certain of the air volume inside NPS 1 pipe.
Since one main has substantially more volume than the other, it should have a larger vent. Looking at the Greening Steam / Gill chart on vents, it looks like the highest current-product main vents out there are:
Gorton 1: .33 cfm
Gorton 2: 1.1 cfm
Hoffman 75: .5 cfm
Maid-o-mist 1: .33 cfm
Since one of my mains is about 2/3 the volume of the other, I should have 2/3 the venting on it. Is the best course then two Gorton 1s on it, and one Gorton 2 on the other? I've also been warned that Gorton's have a max temperature threshold that I need to make sure my return doesn't rise above.
I'm doing this myself, so I'm trying to both not go overboard, and have a second set of eyes on this if at all possible!