The amount of glass in the house has a lot more to do with the unit size than the amount of floor area. When you do a load calculation, you input the Square feet of wall, windows, doors, ceilings, floors and skylights. The kind and amount of insulation. The way the house faces. The volume of the house. The internal loads like people and appliances. The number of fireplaces and people. Only after putting all of that in do you get a load calculation.