Thanks. All the firebricks are actually in place. You might be noticing the large space above the forward recombustion tube and the ceiling of the firebox. After years of use, the forward tube became thin and then started to sag dramatically over the last season. Since making the video, I have replaced the tube. I had to cut the old tube out with a sawzall and, although the tube looked like it was about to fall down, it had a surprizing amount of strength left. Of course, it was cool at time I cut it. Because those tubes get red hot, it is not surprizing they would sag if the metal gets thin.
In the spirit of sharing information for the benifit of others (no flames please), I'll tell you that burning a single piece of CPVC scrap pipe produces corrosive hydrogen choride gas for several hours. That gas, coupled with the high temperatures, can put the equivalent of a few years of corrosion on the inside of your stove in just a few hours. Flakes of corroded metal may spall off the internals making "pinging" sounds as they pop off. Incomplete combustion of chorinated products also produces dioxins (which are carcinogenic). Welding and fabrication skills are helpful in the rebuilding of the internals. On the plus side, it makes very pretty blue flames... so there's that...
