5" x 18" DuraVent DirectVent Pro Double-Wall Galvanized Pipe Length 58DVA-18 This pipe length is designed for appliances tested and listed for direct vent. Features a fully unitized twist-lock construction. Use of sealant is optional unless specified by the appliance manufacturer. To calculate install length subtract 1 1â„2†for each joint. No beads or hems. Provides combustion air and exhaust venting for gas appliances Clearance to combustibles mandated by appliance listing The components twist-lock together for a quick secure fastener-free installation 0.020" aluminum inner 0.018" steel outer Offsets venting obstructions .020†aluminum inner wall .018†galvanized steel outer wall Painted outer walls made of laser welded .018†galvalume steel. Caps also available in stainless steel and copper. Outer pipe brings combustion air to the appliance. Inner pipe exhausts flue gases to the outside. Gaskets or sealants not required (unless specified by the appliance manufacturer).