Several appliances feeding into 1 flue pipe, and they are 2, 4" and 2, 3"pipes, do i understand that i would need a 11" flue or a 9" flue
boiler is a 162,000 btu
furnace is 2 ton
hot water heaters ? standard? one for 1 unit and the other for 2 units
height of flue is adequate ,3' above flat roof of 3 flat bldg. does this factor in with the diameter? could a fan connected to the flue resolve the issue? all appliances have been working fine , but gas co. red tagged it. they were not specific on the fix.