Dual HVAC Unit vs. Zoned Single Unit
We live in Atlanta and looking at buying a house from a spec builder. We are looking at 2 different developments. Both houses are 2 stories with a basement in the 3,500 to 4,000 sq ft range. The builder in one development uses the standard 2 HVAC units that I'm familiar with (one for first floor and another for 2nd floor, and a 3rd one if we finish the basement). The other builder only uses 1 HVAC unit that is zoned (but bigger tonnage). They said that they've done studies and this is the best and most efficient way to go. They won't even give me the option for 2 units if I want to. What are the pro and cons between a single HVAC unit that is zoned vs. dual HVAC units? Based on my very limited knowledge of HVAC system, I was thinking that a single unit is more inefficient as the whole compressor would either turn on or off, whereas with a dual HVAC setup, only the appropriate compressor needs to run as required. Was also thinking of redundancy. In our previous house, the HVAC unit upstairs broke down several times in the middle of summer. We were able to camp downstairs while waiting for the upstairs to be repaired. Let me know what you all think.