http://www.ednasantiqueshop.com/radiators.htm Alan,try this site , i found good info on both types of radiators, hope it can help you out on those you have, most steam radiators have a bleeder valve on top side, to let out air, do yours? is there a hole or plugg there, and also these radiators depend alot on your system,, check out that site it explains way better than i can, good luck..Ron