I don't like it either. I finally got word back from the installer -- they just put the 6" inside the 8". The 8" in crimped into a hole in the liner; the 6" is just sitting inside of it, but the 6" does run in one continuous piece from the stove to the opening in the liner and he said the crimp is fairly snug. The insulation is stuffed between the two pipes at the end closest to the stove. Just one more thing to get fixed... sigh.