EDR for cast iron convector converted from gravity to forced air

Jay Raymond

I am about to replace a steam boiler. There are three radiators but the rest is seven cast iron convectors in wooden boxes in the basement. Originally the air moved by gravity circulation but many years ago supply and return ductwork and a blower were installed to force air through each convection box. How do I adjust the EDR for these? I don't yet have a copy of the EDR guide, so I don't know the EDR of these, but here is a typcial description: the finned tubes are 3" in diameter, 36" long. There are nine rows of tubes and two layers, for a total of 18 tubes in a box. It would also help if you can caluculate the EDR for these and then tell me how to adjust upward the EDR. I am assuming that the forced air increases the condensation rate.