75+ yr od home, North Central Texas (meaning hotter than heck summera), we plan to replace the roof (and raise it several feet) and finish out the attic space. Current duct work (I'm guessing 12-14") is in the attic, leads to each room from basically the center of the house.

We're planning to do the bulk of the work and basic planning on this project. Am I nuts to think I can put the duct work between the floors, so that ground level is cooled from the ceiling and upper level is cooled from the floor? Am I inviting problems by "snadwiching" the duct work between floors like this? Do I need to leave access to it somehow? We've never had occasion to mess with our existing duct work, but Murphy's Law says as soon as I close it up, I'll need access to it.

Is there a smaller ductwork that is efficient? I have heard of SpacePak, which is a 2" duct system. Has anyone used this and if so how did it work out? Are there other systems I should consider? I assume you will have more rapid air flow because of the smaller diameter ducts, but how much faster?

Also, we will probably need a larger AC unit (probably to be located in the upper level). Current system is 15 years old, probably ready to be replaced anyway with a more efficient model, but is there any brand/model I should consider when using smaller ducts?

Thanks in advance!
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