I believe that I have two transite HVAC supply ducts that run under the slab in my living room. I have a "regular" basement under most of the house, but the living room is on a slab. They appear to be in good shape, but I would still like to stop using those ducts. We rarely use the AC and have just put a good gas buring insert in the fireplace in that room. I can shut the dampers to those ducts in the basement, but is there other/better ways to seal those ducts off? Also, will shutting off/seal those ducts screw up the air flow in the rest of the house?