I have posted this in other threads, but would like to add it here.
I built a 6 inch
RMH, and it so happens, that the barrel was located 3 feet away from an electrical panel. Once the mass dried out, and the stove was "rockety" - it was normal too see the top of the barrel hit 1100 F - hot
enough to get the face of my electrical panel too hot too touch - just from the radiant heat coming off the barrel after an extended burn.
You need the barrel to radiate the heat away from the stove - that gives you your draw up the chimney - but when my plastic vapor barrier started to crinkle up and melt - ya know your in trouble ....