Plan #3 is a single story home with a single furnace/air conditioner. The family/living zone requires more hours of heating and cooling than the bedrooms because it is occupied the most, and also typically requires more cooling in the summer months than the bedrooms. The bedrooms may only need cooling in the warm evenings. Without zoning the bedrooms may over-cool during the daytime of the cooling season; and if less winter heating is desired in the master bedroom than the other bedrooms, this would easily be accomplished with zoning.