Convert from 2 pipe to a 1 pipe system??

Steve Weeks

My house was built in the 1920's(??) and has a newer hot water boiler (w/ circulator) connected to an old cast iron two pipe system. Most of the rooms have old 26 inch high 5 column radiators, each with their own spply and return branching off of the main supply and return. Many of the cast iron pipes in the basement are large and low hanging and we're going to finish the basement. There are also two large "dead-end" pipes (a supply and a return) that are no longer used but I assume are full of cold water. To get us the headroom we need and improve the efficiency, a friend suggested we convert the system to a one pipe copper system w/ monoflow tees. The individual supply and return to each radiator would remain unchanged since these are in the walls and would be hard to replace. I wanted to convert to copper but keep it a two pipe system because I am worried about temp. drop as the water runs through all of those big radiators (it's a 2,900 s.f. house). I don't want to spend a lot of $ and end up with a balance problem. Any thoughts?? Thanks.