Hi all , Pls I need second opinion regarding near boiler piping of a steam boiler. We are about to install 2 new steam boilers. 2 Old steam boilers were 2’’ diameter coming out from the boiler to a 4’’ common header and to another 5’’ riser to the attic which circle round the attic area then feed down to radiators. Pls see attached pictures for better understanding. New steam boiler by Weil-McLain LGB6 model come with 6’’ diameter outlet which can be reduce to 4’’. Riser and Header are 4’’ minimum recommendation by Weil-McLian but the supply steam doesn’t have minimum diameter size according to their drawing. However, when I called Weil-McLain tech support am not too convince by their answers I was told they did not test their system for that kind of scenario of mine but they still want to see 4’’ going through the building. So here is my question can I connect my steam supply coming from the boiler 4’’ to a 2’’ tapping that goes into building existing common header which is 4’’ diameter, also that 4’’ diameter header goes into a riser which is 5’’ diameter ( pls see the pictures with label and attached manufacture drawing) in other word I want to run everything in 4’’ exactly what manufacture show in their drawing but at one point I want to reduce to the existing header which only have 2’’ welded FIP on a 4’’ header. Which is the reason am asking the question because it’s a welded header we don’t want to do extra work of cutting and welding if its not necessary. By the way the old boiler was same btu size as with the new steam boiler apart from the design that is different. Also, the steam boiler supply 32 units residential apartment.