Our Ryan homes development is building to Energy Star specifications. These specs changed to Energy Star 3.0 this year. As part of this change there were a few items that were required for Energy Star 3.0 certification for the house, and some of these items change depending on what EPA Climate Zone your house is being built in. Our sales district is based in Climate Zone 4, and our development is in Climate Zone 5. The big difference between the two is in regards to increased R value insulation in pretty much each area of the house (attic, exterior walls on the outside, interior insulation, etc.) Now that's all fine and dandy, but insulation won't balance the house alone. After changing the insulation and ductwork to comply with 3.0 they recalculated the system (probably a Manual J - standard calc and just a guess on my part) and my PM said they could do a 1 zone system with a larger tonnage unit. They also as part of the calculations realized that they couldn't pass 3.0 with the two zone setup that they used previously and had to reengineer the entire HVAC system to work as a 1 zone system. The other part of 3.0 which I figured out by poking around is that the HVAC filters need to be accessible from a common space. The common space requirement I think effectively eliminates having that 2nd zone system housed in the attic.
The other thing I found out is that 3.0 requires gas range venting to vent to the exterior of the house, and explains the no "over the range" microwave thing as well since all of those blow back into the room, and not into an exhaust duct.
All in all it doesn't take away the disappointment, but since part of Energy Star 3.0 is that there can not be a maximum deviation of more than 5.0 degrees from any two points in the house I think we'll be alright. On a side note they may be at the point where Energy Star would be doing the testing themselves when they're ready to perform the balance / deviation test on our build. I think my comfort level with the 1 zone will be OK if I get a copy of that balance test results ( the township even gets a copy of this, what's one more?) and if Energy Star does the test vs. the designated HVAC contractor.
If anyone else out there hears different, please comment. I'd like to hear your experience as well.
There also is the side benefit of only having to maintain one system, one set of air filters, and possibly buying one Nest thermostat vs. two... :)