Big old boiler system - what to do?

Carleton Hecht

Hi everyone - I need some educated opinions on a boiler system. One of my customers is replacing a boiler in a 5-story building. The system is a downfeed system with a 7-inch express riser to the top floor, which then splits into 10 downfeed pipes. All the radiation (one-pipe radiators)on floors 2 - 5 branch off those 10 pipes. His customer wants to kill the top 4 floors of radiation and use a smaller boiler to heat only the first floor. He could cap the express main, but we are unsure what feeds the first floor radiators. Those radiators are fed from under the floor in the showroom - and are two-pipe! ( but no thermostatic traps - just 2 valves! could one valve have an orifice in it???) Near each 1st floor radiator is one of the downfeed pipes disappearing under the floor, so I was thinking they were also supplied off those pipes. BUT,
There are two return lines coming back and one main going through the wall into the area under the showroom where he can't get to.