sq ft heating surface from coils in air handling system

have the following problem?

replacing boiler in old building We have gone around the building and sized all the Rad's

The building has a air system with 2 steam coils. no information onthe unit.

the blower motor on the unit is 3HP

The unit is connected with a mixed air section set 55 deg F


Coil sizes are 66" X 17" 2 of

Any Ideas how to come up with the EDR #


Thanks for any help you can give


Lawrie.