so made a rocket stove to act as a water heater. used 4 inch thin metal pipe AC duct., Worked well first day test run. ran for about 3 hrs.Today was working the a little better due to a shorter up pipe witch lowered the water pipes. After about 2 hrs running 30 min at max fuel scrap wood chopped up to the size of large kindling. I was able 150 gallons a hour up about 40 degrees (from inlet to output).
The metal lining melted and the vermiculite insulation pored in to the combustion chamber...Tried taking out the melted liner and vermiculite just using the block structure not even close barely any temp change even at 25g and hr. So the rebuild will have thicker elbow and combustion chamber. These two sections Melted. the elbow is completely gone.