DuraVent 8860 6-8 Double Wall Stovepipe Increaser Use to increase from a smaller appliance flue outlet to larger diameter chimney or stove pipe. Completes the venting system when used with one of DuraVents chimney products, such as DuraTech or DuraPlus. DVLs double-wall, air-insulated design reduces clearances to combustibles from 18 to 6, the closest clearance to a wall of any connector pipe. Because the inner wall is stainless steel the flue heats up faster, stays hotlonger, minimizes the formation of creosote, and has the same life expectancy as the chimney.