Advice for making my first rocket stove for heating 2+ rooms

Hello!
A little history, as this is at least for me complicated. We have a house, in which one person lives most of the year. It might become three persons at some point in the future. The house is 60 years old, made from bricks, mud bricks, hay, wood beams, not very well insulated in some places. No concrete at all, stone only somewhere inside the base. We use ordinary wood stoves for heating, two normal and one cooking stove. Recently I heard about stoves that do not smoke. After a lot of reading, I am here. I am reading batchrocket.eu and a few more places, so at the moment all of this is very new and a little too much information. I want to be able to heat the house more efficiently, at least for next winter. Sadly money is a bit of a problem. I want heating and cooking to not depend on electricity. And I would have liked to have hot water from the heating, but I think it is not possible in my case.

In the two drawings below (sorry for the not straight lines, I have not drawn in a while) you can see the main house, kind of strange shape. The first image is from top, second is from the side. Not all of the rooms are used at the moment. Only the circled in red two rooms and the two smaller to the left of them. The number in each room is the area in square meters. Those small rectangles with circles inside are chimneys. You can see what kind of stoves we use now for heating. I would like to replace at least the two central stoves with one rocket stove to heat both rooms and if possible more. Since I am familiar with these metal stoves, I am thinking to make a metal rocket stove that looks like them and then put bricks around it to store the heat. Probably will place it in the room 16m2, because it is in the center of the house. For heating the other room, I was reading about getting the hot air from around the stove or from the exaust with metal pipe, which goes through the wall, then inside more bricks, before it goes to the chimney. I do not want to make benches, more like something shorter and taller. Maybe building the stove and channels entirely from bricks would be better, but I think my grandmother will not like it. And it is not portable, in case we change plans. I also plan to make one with furnace for baking, maybe to replace that bottom cooking stove, but it seems a lot more complicated for now.
On the second image you can see that the rooms have different elevation. The chimney for the two main rooms is basically put on steel beam inside the roof of the left room. We recently built extension below it, inside the room, from brick chimney bodies, but they do not support it.
The stove on the third image is similar to what I want to make, without the bricks and will be rectangular in shape. I was thinking about J style at first, but Batch is better for using bigger wood, so it would need less chopping.

I will try to not ask too many questions, so for now this is it:
1. Do you think placement of future stove and way to heat the room next to it is okay?
2. Do you see any problem with the placement and build of the chimney and the different elevation of the rooms? Like if a pipe goes from high to low to high again?
3. Will it be okay if I oversize the stove, but not use all of its power?
4. Any way to heat the kitchen too? The left room with the cooking stove.
5. Is there any way in this case to have hot water from the stove, without electricity? Some pipes in the bricks? We have only normal electric boiler inside the left 4m2 room and do not have basement.

I can add real photos if needed and provide any other information. I just do not have any experience with these things, but I am learning fast and need to do it in the coming months. Any advice of any kind is welcome. Thanks!

Ivan,

Surrounding a metal stove with bricks will not solve your problems. The energy has to be extracted from the exhaust.
I would suggest the following:

1. Cutting opening in the wall between 10 and 16 m2 rooms and building a BBR masonry heater. I saw such solutions.
Please remember that masonry mass provides energy through radiation which would be blocked by a masonry wall. That's why masonry houses usually have separate masonry heaters in each room.
If we know your location, wall thicknes, insulation in the roof, wall openings, we could calculate the heat loss and adjust the power/size of the heater.

2. For kitchen you could build a cooking stove with a small bell to get more heat in the room.

Water will add complexity for a new builder, but it can be done. It would make sense to add it in the kitchen stove.

So you are saying that I should forget about metal stove? That makes it a bit more difficult to accept for the other people, but we will discuss it when I have general idea of size and shape.
My idea was that the stove itself would heat one room and the exhaust will heat the other room.

When you say opening, do you mean small opening just for the exhaust, like 150-200 mm? Because I cannot do big opening. The wall is bearing the load of the roof and the chimney. That would make my life a lot more difficult

Location is north part of Bulgaria. Walls are 30cm, except the kitchen and small bathroom 4m2 above it, they are thinner. There are windows on the south part of the house, I will measure them when I can.
Insulation is basically none. Only the left wall of the kitchen has some, but I think the wrong type. The roof has ceramic/concrete tiles, wood beams, something like clay-hay mix between them for ceiling. I plan to add insulation where I can, especially on kitchen and bathroom external walls, and if possible inside the ceiling.
If it is helpful, I can also measure the temperature difference with low resolution thermal camera. I will also measure all needed spaces, like between chimney and door, and report back.
Happy New Year!

Ivan,

I understand it all better now.
Here is a good heat loss application for Central Europe:

https://cieplo.app/start

You can run it through a translator. Once you know the total heat loss, we can decide on the heater power.

Using the metal rocket and a bell in the larger room could work.

If the wall between rooms is load-bearing, you could get by with cutting a 20cm wide x say 30cm high slot near the base for the gases to flow from one side to the other, without any problems.

As Cristobal implies, the best setup would be a combustion core (J-tube or batch box) in one room, probably the lower one, inside a masonry bell of about half the size calculated for your heating load, leading through the wall to a similar bell on the other side, and then to the chimney. You can build the bells as three sided boxes with the existing wall making the fourth common side, to minimize space required. The core will require certain minimum horizontal dimensions inside the first bell, though part of the core can stick out if necessary. The second bell can be any shape that gives the right internal surface area, such as wide and flat to the wall, possibly projecting as little as 30cm.

Given appropriate planning, you can build an easy J-tube to start with and then convert to a batch box with very little waste when you have more time and experience. J-tubes do not require all of the wood to be split small; the bulk of your fuel after starting can be sized such that 3 or 4 logs will fill the feed tube.

I made more measurements and started to make more precise model in Sketchup. At the moment thinking about DSR2 or Shorty core. It turned out that the walls are thicker, up to 38 cm. However, the wall between the rooms I think might be from mud bricks. That complicates things and does not allow me to use it as a fourth wall for the bells I think. Should I consider insulation between it and the bells?

I put what details I could in that website, however the power required it tells me differs a lot from the batch rocket calculator table. For the same temperature difference, outside -12 and inside 22 degrees, so 34 degrees difference:
- The website says 25 kw for the whole house and 6-7 kw for the two rooms.
- The calculator table is simpler, I know, but it says 11 kw for the whole house with the worst insulation and 4 kw for the two rooms.
Then from the calculator table, do I need the size from "2 fires" or "2 double fires"? I think that puts me in 180 or 200 mm size, but I do not know if it is too big. The specifications of our current stove in the right room, slightly bigger than the one in the left, says 10 kw power, but I am not sure how to compare it to rocket type stove. We never burn it full, because it gets too hot in the room and at the pipes for the chimney.

I am still thinking of the best way to connect the two bells through the wall. That 30 cm elevation is a slight problem. I also wonder, do I need inner chimney for the second bell? So that hot gas from the first bell goes first on top of it inside, then to the bottom?
Is someone familiar with russian kоlpak bells, is that a good idea or not? Like this

I also tried to measure the chimney. All of our exhaust pipes are Ф130 mm, that includes the hole through the wall in the right room. The chimney I think is something like 230x150 mm rectangular, not smooth inside. Is it going to be a problem?

And if possible, advice me on material for the core. Price and difficulty of assembly are important, but I wonder also for abrasion resistance of the bottom. I read about vermiculite board, ceramic board, insulating fireproof bricks, shamote bricks, fireproof concrete. It seems vermiculite is very easy, but very brittle. Concrete is difficult, because it needs molds and vibrating table, I do not have them. Fireproof bricks are expensive and not sure how easy to cut and how strong mechanically. Shamote bricks kind of the same? Ceramic board probably okay? I also wonder if 30mm wall for the core is enough. That is the thickness of the vermiculite boards and thinner bricks. Or I need 60mm bricks?

Sorry about all questions, but I have to think about so many things!

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.

Ivan Penev wrote:However, the wall between the rooms I think might be from mud bricks. That complicates things and does not allow me to use it as a fourth wall for the bells I think. Should I consider insulation between it and the bells?

Mud bricks as in adobe? Sounds ideal, though it might need protection/insulation near the top of the bell.

I agree with Coydon. Mud bricks will be a fine part of the mass. The most that would happen to them at the top would be getting fired to pottery, and even that is unlikely unless the riser exhaust is blasting directly at them. It would not hurt to add a layer of brick or firebrick near the top of the first bell in designs where a firebrick ceiling is advised. Shorty reportedly does not need this. I would not aim Shorty's exhaust directly at the unprotected mud brick wall.

You do not need to conduct the gas directly to the top of the second bell; it will find its way there naturally. It is important that the entrance to the second bell not point toward the exit, so as not to short-circuit the flow.

Thank you for giving me directions for everything. Good to know that I can use the wall as part of the bells. I made some corrections to the calculator and now the power requirement is slightly lower, about 5,5 kw for the two rooms. I guess if I improve the insulation, 180 mm will be enough. So far I am trying to fit 180 mm shorty in the left room, but it is a little too deep for that narrow room. Sidewinder is almost the same I think.

I plan to make the bells from normal solid single bricks. Doing everything from fireproof bricks would be too expensive for me. Do you know what temperatures it can reach inside and outside of the bell? I need to plan how far should it be from flammable materials and furniture. For example, in the left room the ceiling currently is made from OSB. I would of course put some kind of protection. But I also wonder how much heat will pass through the wall in the mud bricks.

There is a reason why folk dont use concrete blocks!
They could be used but they simply wont hold the heat like a dense brick will, concrete blocks are full of air cavities and air is an insulator.
The best option with blocks is to find the vibrated high density blocks that are use for sitting steel on or other high pressure points. Of course  they are double the cost!

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?

You ask a good question. I did not think about that. Then it would be best if I make two separate bells. And put insulation between the back of the bells and the wall?
With two bells, on each of them one wall being insulated to not radiate heat, would I still count that wall towards the whole ISA?

I also saw someone else connect two bells with two pipes, one on top and one on the bottom. Would this be better? I am unsure about the different height, will work on that, but just an example.