fstalfire wrote:OK, so one of the $64k questions and one that may require some engineering......how big should the radiators be and how many in each room or what size radiator to room sq. ft?
About 35 BTU's worth of radiator capacity per sq-ft of floor space should be plenty. Somewhat less if your house is newer and/or well insulated. And after you add all of the rooms up you will know how many total output BTU's you will need from your boiler.
My house has (on average) roughly 28 BTU's worth of fin-tube radiators per sq-ft, and it was built that way in 1964. Most fin-tubes are rated at between 550 and 600 BTU's per linear foot, with the assumption of water coming in at 180 degrees and returning at 160 degrees.
I believe the older classic cast iron type radiators are rated to be in the general range of 150 BTU's of output per square foot of their own radiating surface area, and when used with hot water (180 degree in, 160 degree returning), but don't quote me on this without the confirmation of someone who is more in the know regarding this type of radiator.