First many thanks for your speedy replies. Have had about 30 years experience burning wood in the conventional way (started splitting wood behind my grandfather's woodworking shop at 6 or 7 yrs of age) ; and so my initial response to a RMH design on the screen was " that's not going to work, there's WAY to much horizontal run in proportion to the rise" (and etc , etc ) However, understanding the theory and principles involved, and that, apparently , the things actually work, this would be the greatest advancement in wood heat in a long time. And so I have already started to build one since seeing this 5 days ago. This led to my next concern that the top of a common 55 gal drum, at those temperatures, would soon burn out. I saw a utoob vid where they used sand between two pipes to construct the riser. While this would provide excellent insulation, these pipes would burn out too, leaving you with a pile of sand for a riser. In order to resolve these issues, I plan to make the outside(vertical) part of the barrel of masonry and cap it with a round heavy steel plate. This would allow for some quick heat and allow the "lid" to be lifted for inspection,cleaning, or repair, should it be needed. I've been told by a welder that the melting temp of steel is about 1200-1300 degrees, which conflicts with some of the estimated temperatures I've been seeing online, hence my questions. I also discovered that a piece of 6" chimney flu liner, sold at masonry supply, fits nicely inside a piece of 8" flu liner giving a 2" thick column with an ID of 6" and OD of 10" which should work nicely for the riser. Again thanks for being there. I'm really stoked (!?) about RMH's and have interested friends.