The idea of energy savings with zoning is that areas you are not using can be kept less conditioned than the ones you are. And this can vary by time of day or as you set the zone controls.

If the study and powder room ductwork is close to the master bedroom, then most likely there is not advantage to branching it off to another zone. I would think that the kitchen and great room are probably one one zone on your main level, and the master bedroom on another zone. This is the perfect idea. A -because when you're sleeping you're not in the kitchen, and B-when you are in the kitchen you are not sleeping.

So it will most likely not really matter which zone the center of the house main floor rooms are on. And it would be additional expense to run another zone for them.

Now, if one of these spaces had a different load profile than the other spaces on the same zone, THAT could be a problem. (Like big skylights or lots of western glass) But generally I would think that you are fine as is.

The issue is one of magnitude. Conditioning the least space for the least amount of time uses the least energy. That being said, if the extra included area is small and adjacent to the bedroom, we might be talking a very small amount of energy.

My installer did almost the same thing. They put the guest room on the master suite zone (all beds upstairs) and switched it when we complained. This was a comfort issue but an energy one as well. That being said, there are some downsides to what you want. You will make that zone very small and that has implications for duct adequacy and noise. Our master is a bit loud in high stage and I am getting ready to add more vents/ducts.

The HVAC people are doing 2 things - not listening to us but also trying to keep zones equal sizes because it allows them to put in less ductwork and save money for themselves. I really suspect it is about saving them money and they use their poor communication/organization skills as an excuse. What they did on your house is idiotic except that it allows the ductwork to be simpler.

Retrofitting to make it right maybe complicated if there is not access. They won't run extra ductwork and put more registers in because they have gotten passed final inspection.

I wonder if we have the same HVAC people who are the largest in town?

Thanks for the replies. You've enlightened me to a few things I hadn't considered before....like duct adequacy and noise if I had fewer vents on the Master bedroom zone.

The basement is unfinished right now, but we're talking about getting started on that, so I need to make my decision soon as to whether or not to have them re-route the duct work to the proper (requested) zones. But, we have other issues with them (and the builder) AND the HVAC that we're trying to get straightened out.

Nope, we probably don't have the same HVAC people. Ours is a smaller outfit with a WF address.

Thanks!