As the subject states, came across this concept ont tinterweb watched a few vids and thought I had all the materials needed on my plot to build one of these. My cob is a little unorthadox consisting of sand cement and manure and is taking an age to dry out but is heading in the right direction. The burn chamber and heat riser is in the J formation and made from storage heater bricks. Which brings me to the first question which is, do I still need to put a layer of insulation around the heat riser will it make that much difference? The first problem that I solved thanks to this forum was to stick a vertical flue on the end of it as was getting some smoke back issues all solved now. The issue I have at the moment is that unfortunately as I am doing this on the cheap aka free, the only exhaust pipe I have is twin walled so no latent heat to warm the seating so have not bothered to make any yet, which leads me to my next question where can I source cheap pipe? in the US pipe seems infinatly cheaper than here UK so if any of you guys coud point me in the right direction that would be great.