Selkirk Metalbestos 4RV-RT 4-Inch Bird Proof Type B Top Round Gas Vent Type B, 4 Incap Brick-Red Color | Nonflammable | Provides A Fireproof Acoustic Seal This is manufactured in Mexico Top round For gravity draft venting of LP or natural gas burning appliances Not for wall furnaces or woodburning applications Inner wall aluminum, outer wall galvanized 100 million BTU per hour