Looking for any input from all y'all out there doing the rocket mass heaters yourselves...
I've attached photos of what we've built so far. My brilliant husband as come up with the design based on internet research and what we have available, as well as whatever pitfalls we found in our years of traditional wood stove use.
We want to make sure the logic in our heads matches the actual logic of science.
The firebox is 24" x 13", an old cast iron wood stove from Granny.
He has fitted 18" of single-wall stovepipe for the exhaust riser into the combustion chamber (your average metal drum, used to contain mango juice) which now has a lid and bottom welded on.
Coming out the bottom is 5' of that same stovepipe, running laterally about 2' above the floor (this gap from concrete floor to horizontal pipe will be infilled with sand) and ends with a 90° to run another 16' of vertical rise out our original egress through the roof.
I have marked the two cleanouts with red lines, and the exaust riser in purple. There is brick-and-mortar around the two sides of the assembly facing into the room. Once the sand is in place, pipes will be reset and cob will bury everything from the back wall (aka our stairs) to the front wall (red bricks and cinder block, mortared) all the way to the ceiling.
Should the pipe have more turns? That is is main concern as much is learned from trial and error, and that is not something we already have.
Thanks for entertaining my hobby of writing description, thanks for any input or well wishing in our home building!
We may not have it all together, but together we can have it all
My advice would be to save some time and spend a bit more money on firebrick. Also ditch whatever design you have and go with a true and tested design found for free from Peter Van den Berg's site http://batchrocket.eu/en/. This design is the best and fail safe. As John said, the firebox should be insulated. Do not use metal pipe as the heat riser within the drum, not only does it need to be insulated--this is one of the most important parts of the rmh workings, but the metal will burn out. You need firebrick or perlite riser to offset the temperatures between the inside and outside of the riser. The horizontal run is very small and the vertical pipe does not count towards your total. Also, the space between your riser and the barrel is small. A recommended 12" is the minimum for a batch style rocket stove.
I'm also going to mention that the stove appears to be very close to the wooden stairs. Cob around the barrel will get very hot and could build up heat igniting a wood surface. If you do place a stove in this spot, make sure to put a layer of fireblanket between the combustibles and the stove/pipe to prevent catching fire.
Taking an old-fashioned woodstove and glueing a riser to it doesn't mean it becomes suddenly a clean burning efficient wood combustor. The proportions of the firebox need to be right, the port size need to be very precise and the riser insulated and high heat resistant.
There are some projects been done like this, but the wood stove needed quite a rebuild.