Cristobal Cristo

Mass should be on the interior - this way it works as thermal battery making the building more resistant to temperature swings, preventing quick cooling or quick heating by the elements. It also prevents vapor condensation (behind interior insulation).
Thermal mass works best when the lowest and highest 24 hour temperatures are below and above comfortable temperature.
Exterior insulation on the mass also reduces noise levels compared to interior mass insulation.

Hardik,

The rood structure looks quite pretty but for the house it's too leaky and I do not mean thermal insulation but entry point for insects.
You have two options:

-adapt what you have by adding ceiling planks and filling the void with some insulating material (sheep wool would be nice, breathing and natural)

-change it completely to a new roof, in this case you will need to pour a concrete bond beam on entire wall perimeter; 20-25 cm thick, properly reinforced (four 12 mm rebars with stirrups every 40 cm should be sufficient); you would encase anchors in the bond beam, so the future steel structure could be securely connected

I would prefer the first option - to preserve the traditional craftsmanship, but only if the walls are intact (not cracking) and if the termites never got to the roof structure.

Nick,

I also tried to grow gooseberries and some currants. I had over 20, now I have 2. The problem with shading in summer is that the shading plant has to be quite tall and closely planted to the protected plant, otherwise high summer sun will still reach it. I have tried sunflowers but it was hard for me to make them grow (only the first year worked).
I'm just trying to figure out what to do with remaining gooseberries, ten black berries and elderberries. None of them produce anything and I'm trying to find a completely shaded spot for them, but at the same time I would have to fence them, connect irrigation and I still do not know if it will help at all, because even in the shade, it will be over 100 F dry, windy heat. If not they will have to be discarded, because they only use water and give nothing in return.
It always takes a few years to get convinced that some things will not grow without constant fight with the nature.

I would definitely recommend sunflowers. In your climate they should grow easily and as a side effect they will also produce (but not always) seeds for chicken.

Your room is 45 m2. Fi 175 mm in your climate should do the job. My climate is similar and calculations that I did for a 100 m2 house resulted in fi 170 mm.

Please remember that for the shorty you will need to fabricate the door, for regular BBR you can purchase door and adapt it for the heater.

I would get at least 40% Al2O3 bricks, the higher the better. Wood ash is fluxing the bricks lowering their melting temperature and high alumina is countering it. Because of that wood is a fuel that demands more from the material.
For the riser insulating firebricks IFB 26 (1400 C rating, but 1300 C will also do it).

Regarding long lifespan. Masonry heater builder master that I know recommends to build all parts of the firebox from bricks - smaller elements handle expansion better than large brick slabs or refractory concrete. If you also encase them in a tension frame it will serve for at least 30 years or more, because you live in a climate that will not require intense firing schedule.

If your ceiling is solid masonry then I would not count that any heat would percolate to the upper level.

If you are planning to use the adobe wall as one of the bell walls, how will you tie the other walls to it? It will quickly separate from the mud wall from heat caused expansion. I have used adobe bricks for an interior of an oven and after a year of use they started spalling in large chunks. Your temperatures would be lower in the bell, but at the top the spalling could occur.
When I heat my outdoor cooking stove and the interior firebox temperature is 400 C then the outside is 70 C in the same spot. 70 C is burning when touched for a few seconds. The bricks are 10 cm wide.
You are still planning to build two bells, yes?

Ian Graham wrote:As for  no wood floor under a RMH that sets me back, not even with a sheetmetal barrier like I have under my woodstove?

If the top of masonry foundation walls is close to the floor level, you could place steel rails diagonally in the corner and build a concrete pad. This solution is used in Europe when building a masonry heater in the room corner when the floor is too weak to carry such a load.

2 double fires will increase the power by around 50%, so if you used 200 mm then you could reach 6-7 kW.

230x150 is equivalent to fi 186 mm and since it's not smooth inside I would recommend to not build anything larger than fi 190 mm. It would give you 5.6 kW with 2 double fires. Of course you would enlarge the chimney entry to the system size.

It would make sense to build a vertical canal in the second bell that would direct the gases from the bottom entrance to the top first and then they would stratify and exit at the bottom to the chimney.
I recommend building from hard firebricks. They will last, they will store the heat and radiate it back to the room. I recommend a wet saw to cut them. Cutting hard ceramics without water will easily chip them. If no wet saw is available then I would soak them first in water for a few hours and then cut with angle grinder and resoak them during cutting.

Dareios,

I did not know that you want to have income producing fruit farm.
In this case I would suggest to look for larger plots and definitely with high yielding water source.
Assuming 200 trees/ha with 10x5 (or 7x7) m grid planting, if mature and depending on the species they would produce on average 50 kg/tree, so 10 tons of fruit if everything goes smoothly (it hardly ever does with natural approach). 10000 kg of fruit sold at for example $3/kg would generate $30k. Is it much or not, depends on the lifestyle and if everything is debt free.
In hot summer Mediterranean you will be limited to the number of species that you can successfully grow naturally. At the same time it would be the species that everybody grows - mostly olives and almonds. So to be competitive with a selection of not popular species/cultivars you need water. Closer to the coast or on islands, you will be able to grow larger variety, deeper inland - where the climate is more continentailized (like mine), you will be more limited.

You will have to find out what could grow relatively easily and at the same time people would love to consume it. For example where I live, it's almost impossible to buy quality figs (despite it was a fig growing region 100 years ago). The same for grapes they just taste like sugar infused rubbish. Both of these species grow easily in a right spot so I'm investing in them, expanding every year with the best (and unknown) cultivars. I don't do it for income, but at some point when I have excess I can sell a cutting edge fruit if I wish.

I also recommend the melons and watermelons. There is a huge selection to choose from (I already tried 50 different cultivars and have my favorites) and usually the market offers one kind watermelon and two types of melon. According to my observations, cucurbits are the easiest to grow vegetable in hot summer Mediterranean.

I use my black oven to dry and heat bricks before glazing, so the glaze will dry fast during humid rainy season. I load around 12 bricks per heated oven after all the coals died out. Within 6 hours I have completely dry and hot to the touch bricks. Evaporated moisture is dripping through the door. I can imagine than doing it the same with green wood would produce much more water that would partially soak into the firebricks of the oven, so to some extent it would be counterproductive. It would work with smaller volume of wood and it would be better to use it on pre-seasoned material and not completely green.
Also, I would never do it during the firing session as the exhaust in black oven would ignite the wood eventually.

Charcoal burning would require a different design, similar to coal fired masonry heaters. They utilize grates to provide air to the solid fuel that will not produce any light gases that would form a vortex.