I am considering building a RMH in my basement and have a nice stainless steel 55 gallon drum and an 8" SS pipe that I am considering using as the heat riser that will be insulated inside a 12" heavy gauge steel tube. I have access to a lot of bricks and understand from reading all of the postings that the the first 5' or so of the exhaust will be very hot so I will use the appropriate pipe for that and incase it with cob (I am in N.J. and I think I found clay under a huge uprooted tree that would be enough to mix with sand to create cob to cover that 5' of pipe) My question is after that 5' can I not use pipe at all and use just the bricks mortared together to create a turn around Chanel with the same cross sectional area a as the 8" pipe? At the 90" bend, I will have a sealed removable 3' by 3' stone for clean out purposes.The exhaust through my above basement window will have to be experimented with to have an appropriate draft. Will this work enough to be a good mass?