6" x 18" DuraVent DVL Double-Wall Black Pipe 6DVL-18 This 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. Use with DuraVent factory-built chimneys 430-alloy stainless inner wall aluminized steel outer wall 1" outer diameter Reduces clearances from 18" to 6" for walls Reduces clearances from 18" to 8" for ceilings Sturdy construction to ensure long-lasting durability Creates a tight secure connection in your venting system .016” stainless steel inner wall. .018” galvanized outer painted black.