I promised pics of my steel cored, air-cooled rocket mass heater after its first heating season. I removed some of the cob from around the barrel so it could be removed and the core dismantled and fully inspected and all ash removed from inside the mass. See the pics which follow.
So after heating our old and very poorly insulated house with this steel cored RMH, I am very pleased to see that the core stood up without any evidence of heat corrosion as it seems to have been sufficiently air cooled to prevent such overheating of the core itself, although it burned well and heated the house just fine! Steel cored RMH's CAN perform well IF PROPERLY AIR COOLED!