7" x 24" DuraVent DVL Double-Wall Black Pipe 7DVL-24 7" DVL Double-Wall 12" Black Pipe is designed for installation with minimum clearance to combustibles (6" to walls 8" from top of horizontal run to ceiling). Subtract ¾" for installed length. Constructed with a stainless steel inner wall. Diameter: 7" Length: 24" Stainless steel inner wall Subtract ¾â€ for installed length .016†stainless steel inner wall. .018†galvanized outer painted black.