At this moment, you are the only person who knows whether your floor ducts are part of a slab or in a crawl or anywhere else. It is necessary to describe the location of these things. Can you tell anyone the color of their furniture by typing on the net? Can you estimate the cost of their furniture? Of course not. Describe your situation in full and someone might answer. The greatest cause of misunderstanding among young couples is: "If you loved me you'd know what I want."