This is an inverted V hearth, which has ash for insulation around much of the hottest parts. It uses inert ash to form the upper cone surface. But as you can see, the intake air is cold, not preheated; the hot gas also flows out through a single 2" pipe. This is a major source of restriction in the system.
Here's version 2.0:
The air enters at the bottom in blue, warms up as it flows through the heat exchanger, and warms further flowing past the warm gasifier itself. This preheated air adds substantial energy to the combustion, increasing the efficiency. Also notice the dual pipes exiting the gasifier; these are 3" pipes. They go into the settling chamber, expanding and slowing down. This causes them to release some of their energy to the heat exchanger, and some of the dust settles out. Gas exits near the top of this chamber, again in two 3" pipes, right into the cooling rack.
Another area of improvement is in the lid. I have the whole thing slanted to aid in draining condensate to a collection tank, and a new tight fitting lid is in the works. The lid I made used fiberglass stove rope gasket, which didn't fit particularly well, leaked air to the fire, and caused the gasifier to puff back a lot.
Time to get the old one off the truck. I emptied the gasifier, starting with the ash bin - which I have never emptied before. It was siliconed shut because of a severe air leak. That too is on the list.
The bin is an old ammo can:
Dump! Notice the wood block keeping the can from collapsing under vacuum:
A little too ash-y for my tastes. I would've rather seen more slipped char. It means my grate is not effective. I will be moving to a suspended grate with a grate shaker. The current grate from below:
Once I got it empty and disassembled, into the Metro it went, and up to the house. It comes apart easily into two halves:
I will be making lots of tweaks to the unit in the coming weeks, as well as building the new heat exchanger. Stay tuned!