Satamax Antone wrote:Denny.
You should have thought about the specifics.
He wants to use a masonry chimney as mass. If the wall is half outside, it will heat up the birds. Your case is different. You're making a RMH. Not a batch rocket with a bell. Still, if the bench is against an outside wall, remember to insulate bellow and against the wall, to avoid conduction to the outside world. And BTW, nobody told you yet, that a bassement RMH isn't worth much?
Satamax Antone wrote:Denny, few details.
on this pic, you show the "plenum"
I think it would be good if you enlarged the hole. See https://permies.com/t/61657/Flue-exhaust-transition-plenum-pictures
And i would also cut the top of that pipe lengthwise, except for it's mating end; Raise two sides of that cut to weld under that barrel lid, for a bit more depth. Which would accommodate more fly ash. And obviously make a plug to use as a cleanout.
What length of pipe, and how many elbows do you have there?
Glenn Herbert wrote:Regarding your bench ducting: Unless you use the basement regularly for living space, a bench is less than optimal for heating the upper floor. It needs to be heavily insulated from the floor so you don't lose a lot of heat to the ground. In any case, a tall masonry or cob bell will radiate heat closer to the upper floor where it is needed.
If you do keep the bench, I would say that the duct run is considerably too short to extract most of the heat. A 6" J-tube is supposed to be good for around 30' of horizontal run, with elbows counting for 5' each. I do note the slope to the chimney, which might be partially counted in length. But a bench this size may not store as much heat as the system can generate. If you plan for the basement stairwell to be the main heat avenue, I would ideally move the core to a few feet from it and surround the core with a tall bell, and run the exhaust from the base of that about as you currently have. Heat would have to move the least in this scenario, and be directed more to where it is needed.
Bruce Woodford wrote:You can build a steel core as you originally planned BUT rather than insulating it, you MUST air-cool it! Whenever steel gets over 900F it will glow red hot and corrode very quickly! RMH temps far exceed this but air-cooling on the exterior will enable you to avoid overheating your steel core. See my 7" steel air -cooled RMH at https://permies.com/t/69632/Building-tube-steel-air-cooled for more details on safely constructing a steel cored RMH that will last.