Heat loss Calculation ????

I am in the progress of converting standing cast iton rad's out to a combinations of CI baseboard & panel Rad's.
Are these two types of emitters compatable on the same zone? And in calculating the heat loss how would I handle a small foyer that steps lead up stairs to the 2nd floor large hallway? Would I combine the floor area of both upstairs and downstair foyer in the figures? There is a radatior at the base of the steps and all entrances to the downstair foyer is from heated rooms. This used to be the front entrance to the home but now the front poarch is enclosed and heated, on it's own zone. Should I size out his rad to carry the load for the downstairs and upstairs hallway, knowing that all the heat is heading up there any ways?