Hi again, I decided to also post my question on the heating and cooling forum, so please accept my apologies for cross posting. Here are some floor plans of our home which has almost finished the framing stage. We have made some changes to the plan (i.e. kitchen changes, laudry, moving fireplace to corner, etc) but they are the only reasonable sized plans I can post. The basic square footage and location of walls and closets is quite accuate). Here is the main level. The shading represents the HVAC guy's first plan for drop down boxing on main level, which we will not be doing (our ceilings are only 8 feet so drop downs would really be a drag). Here is the bedroom level. This upper level is over the following rooms on the main level: great room, dining room, main floor baths, laundry and kitchen (i.e. upper level is less square footage than main level). Basement level (full 8 foot basement). This plan cuts of an 10 foot by 13 foot office at top of screen and part of the tandem garage. The study is on one side of the staircases and the garage on the opposite. Thanks for any input on what would work in our floor space to avoid drop downs (or greatly reduce drop downs) in our main and bedroom levels. Also, I would love to hear where others have hidden their vents. Thanks, Carol

Sorry I can't help you with the technical side but I can add my 2 cents about two zones. We have 2 zones - not upstairs, downstairs like you're considering but side by side because we have 2 separate systems. The original house is on one thermostat with it's own HVAC units and the 1000 square foot addition has it's own HVAC system. One important consideration is that placement of the thermostats. You don't want to locate it in a room that is the coldest or hottest because then the temperature in that room will dictate the temperature for the entire zone. We had to move the thermostat because it was located in the room that had the most extreme changes in temperature in the summer and winter. When the thermostat kicked on in the winter to make that room comfortable all the other rooms were too hot and we had to play around with opening and closing the room registers. Another factor is how your house is situated on the lot. Does one side get the full heat of the afternoon sun? Are there trees to provide shade in the summer? Is one side exposed to winter winds? The builder put dual zones in my DH's business office which is only one story but one side was next to the paved parking lot and received the full effect of the summer sun. That side of his office was nearly unbearable in the summer even with awnings over the windows and Pella blinds inserted between the window panes. By making it dual zone they could compensate for the heat in that side of the office without freezing out the occupants in the other side. It might be helpful to get another estimate - and another opinion. As I mentioned I'm not knowledgeable of the technical side - exactly how does the automatic zoning work?

Is this a single speed, single stage furnace that your using? If so there is no way you can hook four zones up to one system like that and expect it to work satisfactorily. The air has to go somewhere, with 2 zones that is set up properly a by pass damper is installed which dumps excess supply air back into the return duct. Many times this by pass is installed incorrectly anyway. With only one or two zones calling there is no way to by pass the excess air without affecting the performance and operation of the furnace. More then likely it will be excessivly loud but I can guarantee the furnace will also be operating alot hotter then it is designed to be. Thats not good.

If you have headroom in your basement I think installing a normal split system and boxing in the ductwork would be the way to go, the attic is the problem you may need to put one or two ductless splits there Here is a link that might be useful: Air Conditioning and Heating Repair Made Easy