I am planning to convert over from steam to hot water boiler hopefully. I would like to run the majority of the new piping myself but I'm a little confused as to how to figure out what size pipe to use. I realize it has to do with delta t's and flow rates but I am unclear as to how that works. I will be be using the oversized cast iron rads I have and hopefully be running 160 degree water. Can any one explain the math to me in layman's terms? Thanks Eric L.