4" x 12" PelletVent Pro Double-Wall Black Pipe Length 4PVP-12B This chimney pipe features fully unitized twist-lock construction. Listed at 1†clearance to combustibles in the USA and Canada. It can be used in both vertical and horizontal installations. Stainless steel welded seam inner wall combined with a galvalume welded seam outer wall. To calculate installed length subtract 1 1â„2†from each length of pipe. Use with pellet oil corn and bio-fuel appliances Laser-welded super ferritic stainless steel inner walls and galvalume outer walls Outer diameter is 5/8" larger than inner diameter 1" clearance to combustibles No additional gaskets or sealants needed The precise fit of twist-lock connections is fast secure and leak resistant. Adaptability is provided by swivel elbow connections and multiple termination options Laser-welded double-wall pipe with a .012†inner wall of corrosion resistant stainless steel and a .018†laser-welded galvalume outer wall. Painted black exterior available. Primary metal-to-metal connection seals joint. Encapsulated O-ring provides a secondary seal.