I had a random little thought about a design, and while I don't have much capacity for tinkering to try this at the moment, I thought I'd just ask quickly to see if anyone else has tried it or could speculate on the results:
In the Rocket Mass Heater, after the flue gases have finished passing through the mass, they are exhausted out. I'm not sure if this part has a name, so I'll call it the chimney, but to be clear, I am not talking about the heat riser inside the barrel.
So, this may or may not be a "newer" innovation, but I recall one of Paul's podcasts which talked about the benefit of placing this chimney directly next to the barrel to stimulate a "pull" draft to complement the "push" of the heat riser/barrel.
One benefit was that the system runs more smoothly, reducing smoke back. An additional benefit MIGHT have been that it enables a longer system? A third benefit was that because these chimneys often seem to be placed between the barrel and the closest wall, they function as something of a heat shield, blocking the path of radiant heat from the barrel and protecting the wall.
So here's my thought:
What if at bench level/knee level, the chimney rose into a T joint, connected on each side to a 90 degree upward turn, and from there, each side had a vertical exhaust pipe running along the side of the barrel? The pipes would look roughly like a tuning fork. The two "tines" of the fork could rejoin near the ceiling (two 90 degree joints into an upside down T joint) before exiting the room, or could exit through two separate holes. (I'm not sure which would be better.)
Would there be any benefit? Has anyone tried anything like this? Is this just nonsense?
My feeling would be that the only benefit, warming the doubled chimney ducts more for better draft, would be offset by the extra bends and be no better or maybe worse than a straight chimney pipe. If you really felt the need for significant rewarming, I would add fins to the chimney pipe for more heat absorption, or run it even closer to the barrel.
When it is used for evil, then watch out! When it is used for good, then things are much nicer. Like this tiny ad: