We are gut renovating a four story narrow townhouse. Our square footage per floor is approximately 680. We are in a row, so only our front and back walls could be considered exterior. Our orientation is generally East/West. We are creating 2 zones for HVAC. (4 zones too expensive.) We are now in middle of debate with a couple of engineers over how to zone specifically. One says 1 zone should be the front of the house, all four floors and the other zone the back of the house. The other says the first two floors should be 1 zone, and the upper 2 floors should be another. It seems to us, that the more cost effective option for heating/cooling bills would be the first two floors 1 zone, upper 2 floors the other. Any thoughts? Thanks!