What is the procedure for sizing main vents in the basement for my steam system. I see a 35, 75 and 77 in the Vent-Rite non-vacuum vents. Each has a different operating P.S.I. I had a new furnace/boiler installed to replace the one from the 1960's and the installer never checked the system and it seems to function poorly. I have read about the need to balance and will be checking the individual radiator vent sizes. Possibly the mains are too small.
Thank you, Bob
In addition to Steamheads comments, I will suggest that you do not change the radiator vents until the main vents have been replaced.
Slow radiator vents coupled with fast, and capacious main vents works best to fill all the supplies with steam before the steam starts up the risers to the radiators.
Post some pictures of your boiler piping so we can see if there are any other factors here causing poor performance.--NBC