New Project - unless it is covered somewhere else on Permies!!
I am working on designing (building soon) a RMH totally enclosed within a 55 gallon drum. J-tube at the bottom, insulated riser in the back. Then the heated gasses do a 180 back down into the drum - making a 90 just above the burn chamber and across the lower 1/3 of the barrel to another 90 degree turn then out the top. All these three runs within the barrel will be surrounded by mass for radiant heat. The top would have a heavy 1/4" plate welded on for cooking or a cast griddle sitting on top. To preserve heat when not cooking a round 2" piece of soap stone or other mass would be placed over the cook surface.
Question: Would a 4" j-tube generate enough heat to "fill" this mass or should it be a 5" j-tube and insulated riser?
I'm guessing a 6" would be difficult to fit inside the barrels space and make all the turns needed.
Secondary idea - rocket stove in a bottom 55 gal barrel with a 2nd 55 gal drum on top that is insulated as a bell. A 30 gallon stainless barrel enclosed in the top barrel as a water heater with three or four hollow stainless 3" tubes welded into the bottom of the stainless 30 gal drum for more surface area to heat the water. So this 30 gal stainless tank will likely be a 25 gallon water heater after accounting for the inner heat exchanger tubes.
This stove could be a 6" box and riser or a small batch box and 6" riser to generate the heat and duration of heat needed to heat 25 gallons of water.
This idea is born from the following requirements:
* Compact design for a small space, but still has some mass to it for extended warmth (fire once or twice a day)
* A gravity fed rain water catchment system will feed the water heater design
* No pumps used - this kind of excludes using coiled pipes that circulate into a holding tank - the holding tank is the heater in this design
If you search the forums for CottageRocket you will find a bunch of threads about that design to help you out.
I'm not quite a lumberjack, but that's OK, I sleep all night and I dream all day; I'll coppice trees, I'll grow my food, and compost poo and pee! With a well and off-grid solar, it's a permies life for me! https://www.youtube.com/watch?v=FshU58nI0Ts