A poorly designed heating system in a room addition has left me with problems. The contractor simply ran uninsulated plastic,such as that used on dryers, into an unheated,un-insulated crawlspace causing the 3 heat vents to receive nothing but cold air. Recently I simply shut the heat vents to the room because it occurred to me that I'm simply heating the outdoors as well as blowing cold air into the room. What I'd like to do is replace the plastic "junk" with insulated ductwork and use the 3 floor vents as return lines since the floor is always cold in the winter. The pre-existing crawlspace is insulated and heated. We also installed a NG fireplace in the addition but it does nothing about the cold floor. I plan to totally seal off the 2 crawlspaces from each other. The old part of the house does not have an insulated floor but I added plenty of insulation to the foundation walls. Does my idea have merit? We don't mind not heating the new room because we use the fireplace when it's occupied and what used to be a window is now open to the room and we had the doorway widened so the temp in the new room stays about the same. [email protected]