One of the things that I have been curious is to, other then the cost. Why not use triple wall pipe? With the smaller jets, I get the room issues, but with the twins and the large jets, I would think triple wall would work. Seems to work well with wood burning stoves. With them, you can touch the outside pipe with the stove burning as hot as you can get it. It's just an extra sleeve of pipe and accordian spacers.