I have a L.L. hearth stove coming in November and am trying to get my fireplace piping ready. I recently removed a woodburning insert and noticed they had a piece of sheetmetal below the damper with an oval shaped hole. I'm going to replace this and my question is should I cut the hole on an angle or cut a circular 6" hole and use a 45 elbow to angle it past my fire shelf? I believe I only have to go about 16" past the shelf but of coarse I want it air tight! Also, it still has the damper frame made of steel intact above the piece of sheet metal. Should I remove it completely as it does affect my clearance for piping and it appears to be held by mortar? I know I will be using stainless steel piping and was wondering any preferred brands out there? This is my first time installing any type of a stove but my fireplace is in great shape, recently cleaned and the 8" clay flue is in great shape.