But if i can put 3 big mouths (10.8 cfm total potential) on a 3/4 tap and have more venting that the tap can actually produce and i can have a 1 inch tap with 3 big mouths which cannot keep up with the potential venting of a wide open 1 inch tap (but not worth installing a 4th), then how much venting can i get from a wide open 1 1/4 inch tap? i just need the next size up from 1 inch tap venting capacity so i know how many big mouths to install on the 1 1/4 inch taps. BTW; i have a 75,000 sq ft apt building with 250+ huge free standing radiators.
Thank you for your insightful reply. Sorry it took so long to get back on site, I got sucked up into another crisis. Yes both condensate tanks are vented to the atmosphere and each boiler has its own feed pump. The current zone valves are honeywell 24 volt, full port and because of their age we are thinking of replacing them when we redo the header (if you have any suggestions on a good durable valve with readily availble parts that would be great). Thanks again