Hello all, we currently have a propane fireplace that we would like to convert to a wood burning stove insert. We pulled the propabe one out yesturday, and now have a shell of a corner fireplace. The fireplace vents thru the wall to outside. What is the best material to line the fireplace with (its bare studs after we pulled the propane) and is it necessary to use triple wall pipe, or is double wall good enough?