The core is 4" and I did a test burn without the barrel. It had good draw. The gap at the top of the core to the barrel is 1.5". The top of the feed tube is missing the top brick. I am planning on filling the gap with cob after I wrap the barrel in copper tube to make a heat exchanger. It appears that the barrel and the start of the 6" exhaust tube get hot, but the mass isn't. I will get temps for my next reply. Thank you
