It seems the smallest practical J-tube is a 5 inch design.
Is a batch box equally limited by scaleing to a small size.
This line of questioning is inspired by: A close friend of mine installed a wood burning stove in his van (he lives in a Van in Wyoming).
It works well except his coals die a bit before he wakes up, so he’s awful cold in the morning.
It would be interesting to try and replace it with
A a particularly small RMH.
Thanks