Don't you also need to know where the OP lives, what design temperatures he desires, and the orientation of the various windows and doors? How about the number of fireplaces and the number of people living in the house?
In central VA - richmond - tidewater area design is 95 F 76 wb.
Fireplaces are negliable since they would not be used for heating purposes. They do contribute to infiltration due to stack effect if the damper is not closed.
For a family of 4 thats 450x4=1800 mbh total or .15 tons.
Hopefully the sketch would have a north arrow, but you're right need the orientation of walls too.