Hi everyone. I have a quick question about venting my soon to be new pellet stove. I tore out my prefab fireplace last week and am buying a harman accentra insert. The old chimney came right out but there's still a 8" lining running up to the top of my roof. i plan on running 4" vent pipe right through this. I assume I have to have a seal of some sort at the bottom and maybe top of this 8" liner. My question is what would I use to seal this?