Watched the rocket stove video. Very nice. Thank you.
The issue you mention at the end is an easy fix. Here’s how.
Rotate the J-tube 90 degrees left or right, perpendicular to the stove, and leave it at the front.
Have the exhaust/ heat access the barrel of the stove above the midway point of the barrel, ON THE SIDE. Place a piece of metal, to form a
Spiral around the barrel 6-8 inches wide ( like a grain auger) that directs the heat from the j-tube over the barrel and around it in a spiral till it exits
Out the back. If you have enough draw, there should be a NO problem.
The area in the rear behind the oven also has enough room for at least five to ten gallons of water, and the exhaust
can come out the back instead of the top, if more room is needed.
This solves the problem of uneven heat, short chimney and my lack of other contributions to the cause so far.
I’ve used the rocket stove to great effect up here in Canada.( because I hated the constant management of the fire, I was able to place two 2x4s in the firebox of the j-tube, and walk away, it burned slowly while the wood sunk into the fire — taking 4 hours for 44 inches approx. The downside is that it didn’t always sink into the flame because thw wood was too light, and that is a safety issue).
As well, I experimented with small chimneys. Used an old style chimney liner that was about 4 inches in diameter. Got lots of heat.
Maybe experimenting with smaller J-tube diameters would be a positive thing.