Insul-Plug Insulated Chimney Plug, available in 6 and 8 inch sizes
InsulPlug blocks stovepipe holes after the original pipe has been removed. It provides a thermal break from combustibles and prevents downdrafts from entering the room.
InsulPlug is made of a ceramic base fireproof insulating material. It installs easily -- just push InsulPlug into the stovepipe or masonry opening. When the face plate meets the masonry chimney, tighten the draw bolt with a screwdriver.
InsulPlug sides expand and create a tight fit inside the pipe opening, Can be removed by reversing process.