I have a MetalFab telescoping double wall stove pipe attached directly to the top of my stove. It's fastened to the stove top flange on the bottom and a 90 degree elbow on the top. When the pipe cools it contracts and decreases in length and puts pressure on the various connections leading up to the ceiling support. Are the two sections of the telescoping pipe supposed to be fastened to each other? The instructions don't mention fastening other than the ends of the pipe assembly.