Sorry if this has been covered before, but I did do a search on the forum and found nothing related. I think I know the answer to this, but I can't rule it out until I get a sanity check. My home could really benefit from zoning to manage different levels of the house. The trouble is that the supply duct work is too intertwined between the floors to separate. Redesign & replace of supply duct work means ripping out ceiling and wall sheet rock not going to happen. The return air, however, is cleanly separated between floors and would require just two control dampers. I've never heard of this being done, so can I assume that it is unwise to pursue that approach? Ineffective? Cost prohibitive? Unlikely to find contractor experienced in such an approach? If it matters, one floor uses a round duct (about 12) and the other is rectangle (estimate 10x16).