I want to put in a gas fireplace. I currently have a wood burning fireplace that sits on a concrete slab. We put an outside air source in the floor connecting the fire box to the cellar. It drops 12 inches vertically and then makes a 90 degree turn and goes straight to the cellar. I think copper pipe will crimp and not make the turn. Has any one used or know of a flexible alternative to copper. I use propane from a tank outside the house. I'd appreciate any help you can give me.