My house has a two-pipe, single-loop hydronic heating system with cast iron radiators. I want to add a small cast iron radiator to a new 2nd floor bathroom. The pipes are all black metal with cast iron fittings. How do I tap into the 2.5" O.D. pipes in the basement to run new lines to the 2nd floor. I could tap into nearby lines to other radiators, but I'm thinking that may not be very efficient. I could also remove ten-foot sections between 2 other radiators and tie in a T with 2 shorter lengths on either side, but am concerned about frozen and brittle cast iron fittings. Any suggestions?