Steam heat vs Hot water heat
Wow... you're really mixing terms in your first post, and I'm sure that you don't even realize it.
A radiator is the cast iron things, and a convector is the fin stuff that you run along the baseboard.
You can really, really, really, really, really screw up a system if you arbitrarily add or delete radiation and change the size of the radiation in a steam system. The size of the installed radiation has to damn near equal the steam capacity of the boiler in order to have all the radiators filled with steam and to recondense the steam to water. I wouldn't go fooling around with changing the radiation to a different style unless you've had a qualified steam heating contractor or heating engineer calculate the EDR required for each room and in total. You'll be in a world of hurt if you do this on your own arbitrarily without calculating exactly how much of what size of the new type of radiation you propose you need and where.
You can very easily convert a steam boiler to a hot water furnace by the elimination of a few controls. Unfortuneately for you, you have a one pipe system, so you'll also have to run more pipework. A hot water system requires much, much more convection surface area when compared with steam radiation.
I don't want to discourage this project. I only want to encourage you to seek the assistance of a steam heating contractor or a heating engineer to look the place over, do the calculations, and spec the radiation for you. It's nowhere as simple as hooking something that's prettier than the old one to the end of the pipe.
Perhaps you will consider just having a sandblast contractor blast the existing radiators to bare metal and repaint them? Many turn of the century buildings still have their original radiation installed, even though the building has been rennovated many times. Sometimes it's best just to leave a good thing alone.
Last edited by mdshunk; 10-02-2006 at 10:16 PM.