Doubts before you start building!

It is the first post that I write in the forum but I have been researching and reading in it and in other spaces such as donkey for some time, I also read Ianto and Leslie's book, as well as Annex 6 by Emie and Erika. I was in contact with Erika and she advised me to post here. Thank you all in advance for your help.

I am in Spain, in the region of La Vera in Extremadura. A Mediterranean climate with a lot of humidity in winter and temperatures that do not usually drop below 3 ° C. I am currently finishing building a small stone, lime and esparto hut. It is a circular construction with an interior area of ​​approximately 8m². (Although it is a small space, I plan to live permanently in it and build in the not too distant future, some more module to cover shower, toilet and storage needs). The wall is made of stone up to 1 meter high and is lined with lime mortar. The roof area is a dome built with lime and esparto (tufts of esparto bathed in NHL 5 hydraulic lime mortar) on a chestnut branch structure, this structure has been removed later, although in some areas it remained inside the wall. All this is built on a foundation that separates it from the natural soil by a layer of hydrated lime mortar, two layers of gravel, thin and thick, a total of 40cm thick and sealed with NHL 5 hydraulic lime mortar.

I would like to build a rocket stove. Due to the opening that remains for the outside chimney, about 14-15cm in diameter, it can be a 6 "system, perhaps a smaller one if it generates enough heat, but from what I understand the 4" system does not allow it to be accumulate heat in thermal mass. The problem I have with the 6 "system is the total height of the factory. I understand that the ideal measurements for an elevator are 90 cm, for me this is too high because with the height of the barrel plus the insulating base of the floor in addition to the The thickness of the bricks would be around 1.10 meters high, which is a lot since it would touch the dome and I did not have space to cook, so I think that the measure that suits my needs would be a 70cm riser that would give 46cm. burn tunnel and a 23 cm loading zone, right?

Another problem I have is the material, I am currently in a very tight economic situation, I know that the ideal is to build the core with refractory brick of 40% alumina, which is very expensive. Now I have material that I could use, some refractory barbecue brick, which is not solid. Could I fill it with clay from the ground mixed with crushed remains of refractory ceramic of 1259 ° C? I also have quite a few normal building bricks and 10 bricks from an electric accumulator system. The firebricks he had planned to use in the burning tunnel. The riser planned to build in clay with pearlite (balls of clay spread for construction). The accumulator bricks I think would be fine for the thermal bench then lined with and maybe I can get a granite slab. How do you see it?

For the barrel, I still do not have it but I think I will be able to get a 300L with a lid and crossbow closure, if I cannot get it I have a round stove 35cm in diameter and 53cm high, do you think I could use it here? If I get the barrel, could I build the riser with normal bricks filled with refractory ceramic and clay from the ground? The barrel or stove might radiate a lot of heat for such a small space, could it be lined with cob? (I guess leaving dilation and contraction lines for heat and drying, right?)

The bench would be a bell approximately 70 cm long by 40 cm wide, assuming that it will not be a rectangle due to the circular shape of the house. This would come out through a horizontal section that would pass under the barrel and between the wall of the hut and the core to be joined with a vertical section that could be built in common brick, filling the holes with clay that would rise to the opening in the dome where It would be joined with a metal pipe, the pipe on the outside will be lined with mud and straw and this lined with lime. Do you think that on its way through the dome it could have a problem with the esparto that is inside? If there were a possible problem, I would have to reduce the diameter of the tube so that it is not in contact with the lime mortar and esparto grass, could I use a piece of sheet metal to make a cylinder of about 14 cm in diameter, could this produce a plug? If this creates a problem, you would have to reduce the system to a 5 "or 4" one, then you could not have a small bank, like the one described above or smaller?

To all this I am off the grid without electricity nor possible to get now.

I will try to upload photos of the material and the hut.

Hi Diego;  Welcome to Permies!

Well that is a lot of information, let me give you some answers and alternative choice's.

First I will ask were you thinking to build a traditional J tube rocket mass heater?  
Next I will ask do you know about batch box RMH ?
Here is a website that tells all about batch box's  http://batchrocket.eu/en/
A batch can be built in 5" and even a 4".

Next I want to give you my highly recommended choice. Walker stoves has a riserless rmh!  No height problems at all. And they are set up around cooking.
Here is his website http://walkerstoves.com/index.html
Go to his site and check out his tiny masonry cook stove heater. I think you will like it.
Matt just sells you the plan. You use local materials and build it your self.

I realize you said that money is tight and you may not be able to build a riserless core right now, but I wanted you to know about the possibility.

So I will try to answer a few of our questions.
Yes I think the BBQ brick with the holes filled, with crushed refractory and clay will work.
Firebrick for the burn tunnel is good. A perlite clay riser is a good choice.
Regular brick can be used after the core, even concrete block can be used to surround a mass.
I think no problem with the pipe being near the esparto. Pipe temp will be low.
A clay brick chimney going vertical will work as well.

Thank you very much Thomas for your reply.
Lo I will answer your questions. if I'm thinking of a traditional J rocket. I was studying the possibility of a batch box but I think it is more technically complex and I may need material that I do not know if I can get at the moment, such as the door. could it be built without a door? if so, would it be efficient? and dangerous? So, if you don't have a door, you don't need channel p?
the same thing happens with the Walker system. I don't have a way to do the cooking plate and the door. I also thought that it was necessary to build it with refractory material and of good quality given the shape. But if I find a way to get a door and a kitchen area, it may be better than a J system or a batch box and I do not rule out doing it but for the moment the material I have I think is more appropriate for a J system with dough.
I will be attentive to what they suggest. Thank you