PelletVent Pro 4" x 24" Galvalume Pellet Stove Chimney Pipe - 4PVP-24 This product requires: 1 (3 in Canada) air clearance to combustibles for all diameters. Joint/Connection Overlap: 1-1/2. Joint/Connection Type: Twist-Lock standard on all diameters. Outer Wall: Galvalume Laser Welded. Inner Wall: 304 Stainless Steel&#44; Laser Welded.