Fortunately I live in an area of Patagonia where currently there are with no building codes. Rather I have a friend who has property in a rural area that is not monitored (yet). The towns have building codes.
I think one of these rocket stoves would be perfect for her small cabin as her wood stove is fast consuming the amount of wood on the property.
However, I don't want to build one in a permanent way (cob, concrete) and then have to tear into it in a year or two due to problems. Once I build a permanent version I would like to have it be relatively maintenance free for 10-20 years.
Here are the parameters I would like to build to:
1) For the test (year or two), I would like to build one that did not require cob. Is it possible to have the heat mass be sand? What are the implications of expansion and contraction for the box (probably brick) that would hold the sand? Would the sand expand crack the brick box or compress the stove pipes?
2) What are the experiences and expectations of corrosion in the metal pipe through the mass? This is quite a length of pipe, and were it to corrode in the cob, what are the implications? One would have to deconstruct the cob and rebuild the stove....
2a) What about having the exhaust channel be mortared brick instead of metal? I suppose only the entrance would need to be firebrick. What about expansion / contraction with the stove mass, if it were sand?
3) The construction here is already with a concrete slab floor. I would want to insulate the stove from the concrete floor.
4) The walls of the home are single brick. I would also want to insulate the mass from the wall. Either hollow bricks (ie. terra cotta chambered brick), rigid insulation, or wood boards.
Hollow bricks (i.e. chambered/channelled terra cotta is very common here....). I was surprised to find out that they are fairly efficient, when the channels are external horizontal in wall construction as there is no vertical convection current inside the wall.
I am thinking of putting two chamber hollow brick (see photo), the wide side flat, UNDER the heater mass to keep the heat of the mass from the concrete floor. Something similar for the brick walls.
5) Has anyone designed a burn chamber that takes outside air?
6) The cabin will eventually have more rooms on the first floor. I am thinking that getting the heat from the mass into the other rooms is going to be important...and into the bathroom also. One way to do this would be to circulate water with a simple 12 volt pump through standard metal plumbing pipes in the heat mass and carry it to the other rooms where it could go through a radiator or warm another heat mass.
7) I have seen rocket stoves on Youtube where the burn chamber, rocket, and outer heat skin are all welded. This might be a good solution for a long lasting stove...comments? The thicker heat skin would require more heat to bring to operating temperature, but it would not be wasted heat.
Seems to me that on the output end of the rocket, just before the final chimney, would be a good place to have a small chamber to prime the air flow through the ducting in the mass when starting the stove. Is anyone doing that? Starting a small ball of paper then closing the chamber to start the air moving?
9) What are the considerations for making one of these with a long, maintenance free life? Included in this is a construction where if there were a problem it would be easy to fix.
10) How well does the cob mass work? Does the expansion / contraction crack it? How would one know if the metal pipe were to corrode? And what could be done if the pipe corroded?
Thank you in advance for your ideas and conversation.