RMH challenge for house in Sweden

Hello.
My name is Armin and I live with Sabine in Sweden.

This is my first post in a forum, so I apologize in advance if I do something that is too complicated, illogical or otherwise wrong. Thanks to Permie's assistant Jules for the kind instruction. Also sorry for my English, I hope that I can express myself with google's help in a way that is understandable.

We have a small house and we urgently need a stove before next winter comes.




I've read quite a lot about RMH and watched videos, but the more information I get, the more confusing it gets. At first I thought "oh good idea and so easy", but now I'm not sure if I can even do it. I'm an artist and craftsman but not an engineer at all. I'm fascinated when I read the posts about your incredible experiments, but after a short read my neurons knot.
So I decided to ask you for help.
What would you do in my specific case?

Attachments! I have attached all the photos and the whole document as a PDF.

Many thanks in advance


This is the room that needs to be heated.



This is the space available to me.






Here comes the challenge
The oven should:
-heat the room quickly
-keep the heat as long as possible
- need as little wood as possible
- not need to be constantly reloaded
- be easy to build

The floor area of the house is not particularly large at 50 square meters and the room height is normal at 2.3 meters, so the entire room wouldn't actually be that difficult to heat... if it weren't for this big, beautiful "hole" in the ceiling.



This makes it a little more difficult to keep the lower part warm. What we need is a stove that stores as much heat as possible for as long as possible and uses as little wood as possible. We live "in the forest" but unfortunately don't own one and so we have to buy firewood. It would be ideal if the oven could do both: on the one hand heat up quickly and on the other hand keep the heat for a long time. In the morning it should be a little more than just 6 degrees Celsius, as it often was last winter.

on this picture you can see the dimensions and structure of the old fireplace and how much space the oven approximately can have.
 

Armin, you have not asked for much!
I think perpetual motion may be easier than you wish list.

Here comes the challenge
The oven should:
- heat the room quickly
- keep the heat as long as possible
- need as little wood as possible
- not need to be constantly reloaded
- be easy to build

As an Engineer I have an insight to building things, I have a few questions;
1 How do you define 'quickly'?
2 How long is ' long as possible'?

The last three wishes also need definition.
The following are areas I would work on at the same time your heating systenm is being sorted out.
1 Eliminate all air leaks in the building
2 Maximize the effectiveness of insulation.
3 Consider blocking that hole in the ceiling during winter
4 Can you start growing a wood lot?
My own home in Australia is about 80 sq. M and winter temperatures get down to about zero, with many mornings at 6 deg. C.
I rarely heat it, in part because I am comfortable down to about 8 deg, currently its 13 deg.
But all the above steps have been carried out. I get a bit of sunlight during the winter which warms the house, but I often leave the doors open during the day
so it does not always start the night with an elevated temperature.
I dress accordingly but friends do have trouble with it, wishing to sit around in winter in light clothes.
I use a term, 'season changers, who want to chill summers down to 20 deg. and lift winter temps to 25 deg, wear the same style of clothing all year,
and then complain about the cost.
Rocket Mass Heaters are not complex, I suggest buy one book published recently or study this site for the layest designs and just start.
Others can give you more accurate costs for your area.

Armin Speiser wrote:The oven should:
-heat the room quickly
-keep the heat as long as possible
- need as little wood as possible
- not need to be constantly reloaded
- be easy to build

Hi Armin,
I'd think you might need some explanation what a mass heater is and how it works. A pure mass heater is a big piece of (mostly) brickwork that warms up quite slow and cools down even more slowly. Because the cooling down is so slow, the next morning the temperature in your small house will still be well above the asked for temperature of 6 ºC. I'd think 16 to 20 ºC is more likely.
The heat generated by a mass heater is mostly radiation which means it comes off the heater's walls at right angles, more or less. That you have a mezzanine (the large hole) for a large part doesn't change this behaviour significantly. Keep in mind, it's not the air you are warming directly, but the walls, people, furniture and so on. The closer you are to the heater the warmer it'll be.
All this means the room is still warm in the morning. Run it with one load (approx. 1 hour) and go to work or whatever you do for a living. Depending on the mass of the thingy you'll get a cool-down period from 12 upto 48 hours. If you are able to light a fire in both the mornings and evenings a maximum cool-down period of 24 hours is very convenient. In fact, the thingy won't cool down for an entire winter when run at least once every day.

Now the things you mentioned the heater should be capable of:
- Heating the room quickly is not necessary because the room is still warm.
- Keeping the heat as long as possible begs the question for how many hours.
- Using as little fuel as possible can be done with J-tube rockets and batchrockets alike. No smoke means all of the burnable material is converted into heat.
- Not being fed constantly points in the direction of a batchrocket, I'm inclined to think.
- Easy to build won't be possible if all the above demands need to be met.

As I pointed out above, the big, beautiful hole in the ceiling won't make it difficult to keep the lower part warm, at all. One build of a batchrocket on the island of Mallorca was in a house that was bigger than yours, with little insulation and a warmer climate. It sported a large mezzanine and despite the fact that the heater was situated right under the high part of the room of about 7 meters it didn't throw up problems like you described.
Have a look at https://batchrocket.eu/en/designs#squarecore

Never heard of batchrockets before? Please read all of the website, not necessary all of the nine languages, of course.

Based of what I can see and the assumed size of the chimney (18 cm square?) I'd say you could build a 18 cm batchrocket system. That system size is based on the chimney diameter, all other measurements are related to that.
Please, post the size of the bricks in Sweden, what lowest outside temperatures you get, what the height and size of the chimney is plus if and which refractory materials are obtainable.
Two years ago I coached a Finnish guy through the build of a large system with commendable outcome.

Armin;
You are lucky enough to have attracted the attention of the most accomplished Master builder of us all.
If you are able to follow his suggestions, you will have a snug warm home this winter and for many winters to come.

Tack so mycket, swedish for thank you so much for the answers. I will now think about your information and suggestions and will get back soon. Thanks again for the great work you are doing.
Wish you a nice day, wherever you are! Armin

Hello Armin, welcome to Permies.
You have a beautiful house (I'm also intrigued about the roofing tile use on your garden beds...) I'm not experienced in RMH either however....I'm thinking that a batch-bell heater will suit your house. Can you extend the fireplace into the room at all? I'm imagining using the existing chimney as the back of the bell with a new front and burn chamber. It looks like from your picture 3 that is what you are imagining too? I look forwards to your project progress.

Hello everybody!

The subtitle for this project could be "The First Time".

First time trying to build a stove.
First time in a forum.
First time I am asking for help for a project.
First time that I try to be prepared befor i start a project.
Because when I have an idea, I usually take a deep breath and jump into the great black hole of the unknown.
I wanted to be as prepared as possible this time.
Mainly because I don't want to waste your time

So it took me a little while to get back.
In the last week I've been trying to understand the Batchbox system a little better. Among other things by watching many videos.
At least now I know what flames look like in a batch box rocket stove 😉
So I am now at least familiar with the basics of the batch box.

All of this preamble shows the respect I have for this project.
Yes, I'm a little nervous.
But your words and especially the fact that you, Peter, have offered me your support have given me a huge boost of confidence and energy.

I have again attached a PDF with the new information and pictures.

That's all for now.
Thank you for reading this far.
I wish you a good night or a nice day...
wherever you are.
Armin

From the pdf:

Now I have two small questions.
-In the videos, the stove is always quite loud. Of course through the microphone. But how loud is such an RMH?

The batchrocket's sound is a low, rumbling one. To me, it isn't loud, although I'll keep hearing it from all over the house.
In the steel barrels this is much louder because of the resonance, moreover since it's also used as an open system. To most people the sound of a heater without barrels is strangely reassuring, plus it could be operated by listening to it. When the sound disappeares, it's time to have a look at it.

-In some videos i have seen two chambers on top of each other. What is the second for?

That's used in two later models, namely the Double Shoebox Rocket mark 2 and 3. In fact, the riser is horizontally on the firebox. Both are rather complicated for a novice builder, for that reason I won't recommend it to you.

Regarding the placing: in the 90 cm width would fit an 18 cm system. The firebox built out of 50 mm thickness firebricks, the riser out of 25 mm firebricks, both on it's side. The bell around it like the Mallorca build, normal red bricks on flat upto the top end of the riser and above that the red bricks on it's side and a liner of superwool and firebricks at the inside.

Depth is a little bit more tricky since part of the old heater is still there. You'll need to break that down until only the chimney part is still there. The chimney entrance should be lower than the opening is now, the rear wall of the bell could be made of normal bricks as well, placed against but not touching the chimney bricks. This is necessary in order to avoid cracks in the bell and/or chimney due to different expansion rates. I would think the depth of asked-for 60 cm of the bell itself cannot be achieved, more like 90 cm.

One chimney channel is (probably) large enough to serve a 200 mm system but that would be overkill for your petite housing. Moreover, it would take a lot of space also.
Are you prepared to do a lot of demolishing of the brick part in the house and do a lot of building work?

Hello everyone!
Hello Peter!
Regarding your last question: Yes, I am now willing to do what is necessary.
With the new information, the whole project begins to take shape and that means, dozens of ideas and possibilities popping up in my head. I have to organize my thoughts first before the young horses goes thru with my brain... (Is that understandable in English?)🤔

I now, i now! Keep it simple and stupid! It must heat up the house but don't fly to the backside of the moon.😉

Just to make sure I got it all right here is a quick recap of the dimensions.

Risers:
18cm system refers to the inside diameter of the riser. Is that correct?
That means: riser inner diameter 180mm + firebriks 25mm *2 = total diameter riser 230mm. Plus the insulating wool. When building a square riser.

If i build the riser in the octagon about 30cm???
Image octagon riser:

https://drive.google.com/file/d/1Qrzl7BPgxM3-xxY-pJZDHs4gt-MXiPCf/view?usp=drive_link

source:
https://batchrocket.eu/images/rockets/brick177-8sb.jpg


Alternatively, I found this.

Image round riser:

https://drive.google.com/file/d/1NXOVe5uyLl9te-UN06V4kaMQYPv3231e/view?usp=drive_link, https://drive.google.com/file/d/1pED7buSz9TdgRVSwud6pJWKE1v23h4nV/view?usp=drive_link

source:
https://www.schamotte-shop.de/schamotterohr-dn-180x300mm.html

That would make everything much simpler and more compact and the costs stay about the same.


That means risers up to 300mm depth.

Batch box:

Based on the ratio formulas (see below or this link: https://permies.com/t/40007/Results-batch-box-thingy-Innovators#311498) , I calculated approx. 520mm.

This means that the inner core (batchbox plus riser) needs a depth of at least 720mm.
Is that correct so far?

Now a more general question. I've always heard that a brick stove first has to dry for months and can then be lighted up very slowly and carefully over several days. In the videos seems that the RMH are always lighted up directly. Is this right?

Thanks.
Best regards! Wherever you may be!
Armin

Given: Heat riser DIAMETER = D

Base B = D*.72
Riser Height = 10*B

Box Dimensions
Width = B*2
Height = B*3
Depth = B*4

Port Dimensions
Width = B/2
Height = B*2.2

P-Channel Dimensions
Width W = B/2
Height (thickness) = ((3.14(D/2)^2)*.05/W

Armin Speiser wrote:Risers:
18cm system refers to the inside diameter of the riser. Is that correct?

Yes. In case of a square riser the sides should be 18cm as well. The square tube is comparable with a circular one, aerodynamically speaking.

Armin Speiser wrote:That means: riser inner diameter 180mm + firebriks 25mm *2 = total diameter riser 230mm. Plus the insulating wool. When building a square riser.

Forget about the octagon riser, much too complicated for a brick build.
A circular riser could be done with that kaminrohr, although it will certainly crack. Not because of too high temperature but uneven heating instead. There's a way around it, with some succes: make one lengthwise slit in every tube. By doing this, it's already pre-cracked so there's a good chance it'll stay in one piece. Not quaranteed, of course.

Armin Speiser wrote:Batch box:
Based on the ratio formulas , I calculated approx. 520mm.

This means that the inner core (batchbox plus riser) needs a depth of at least 720mm.
Is that correct so far?

Not quite. The back wall of the firebox need to be 50 mm at least, the same as its sidewalls. So it will be roughly 750 mm of depth so far. Plus the back wall of the bell, 114 mm and some leeway for the riser to be free standing. Together 900 mm, as I mentioned before.

Armin Speiser wrote:Now a more general question. I've always heard that a brick stove first has to dry for months and can then be lighted up very slowly and carefully over several days. In the videos seems that the RMH are always lighted up directly. Is this right?

Although not entirely right, I always have done that, yes. Drying for months is a waste of time in my view, better to have one half load a day for a week, than another week with a somewhat larger daily load. And another week with a full load a day, when that's all done, the heater is certainly a good way to getting bone dry. And the best build of all: ready for firing when autumn is coming in, so you'll be able to burn gradually more as the winter's coming nearer.
As long as the heater contains moist, it'll cool off fairly quick. When dry, it'll hold heat much, much longer. So don't be disappointed when it's cooled down the morning after the glorious fire...

Now a more general question. I've always heard that a brick stove first has to dry for months and can then be lighted up very slowly and carefully over several days. In the videos seems that the RMH are always lighted up directly. Is this right?

Not so many years ago my wife decided she needed a wood-fired bakery. The construction began (with a lot of help from the Forno Bravo community forum). Long story short, and to your point, when I first lit the monster it was with a few small fires over a period of about a week. Then I said, "if it's going to get hot, now's the day" and threw some wood to it. The oven took several months to build and I sort of thought that it was "dry," but as all that masonry began to actually heat, water began to be forced from the hundreds of pounds of mass and was actually dripping down the outsides of the structure, and steam was rolling out. The arched roof reared up like an angry dragon making about a 1cm gap between the oven ceiling and supporting front wall. (A bit of that is visible on the left side of this image.) (A few more pics.) When the oven finally dried out and cooled, the arch settled back down to where it belonged with no apparent additional cracks in the structure and no further "excitement" in subsequent burns. We've since used the oven quite a bit with no other issues. Fun build with a couple of exciting but uneventful first fires.

I'd advise following Peter's suggestion with a few small fires to sort of dry things out a bit, then let it rip. I actually do the same thing every season with my Hearthstone wood fired heater just to get the annual humidity/moisture out of the soapstone and prevent cracks.

Thank you Peter for the answers.
That's exactly why I'm here.
I like experiments, but if a project has to be successful in one go, then it's good if you have someone who, thanks to a lot of experience, can tell you, „do it this way“ or „forget that“, and ideally be able to explain it briefly and clearly.
Like the shape of the riser, for example. After everything i read i thought it had to be as round as possible to create the vortex and that a perfect vortex is important to reach the desired temperature and performance. But now I can continue to concentrate on building everything as simply and stably as possible
In the next few days I will get the fire bricks and the bricks for the bell and try a test setup.
Could the bricks for the bell be plain bricks? Is it ok if I use old used ones like those in the attached picture? That would be a lot cheaper than buying new ones.
I will now need a few days.
Have a nice day
Armin

Hejhej Leslie!
Thank you for sharing your experience with me.
This is really a very nice pizza oven and what comes out of the oven is even nicer. 🍕😋
Such an oven is also on my list. Unfortunately still far below.
Greetings from sweden.
Armin

Wow!
I just noticed now that there are 4 apples next to my name.
Thanks alot!
That gives a lot of energy on a cloudy morning!
And because you are also doing such a fantastic job, the whole permies staff/team gets a cake from me and Sabine,
with freshly picked blueberries from the swedish forest.
Have a nice day! Wherever you are!
Armin and Sabine

Armin Speiser wrote:Could the bricks for the bell be plain bricks? Is it ok if I use old used ones like those in the attached picture? That would be a lot cheaper than buying new ones.

The trick with the construction I suggested is the use of much ordinairy bricks, also called red bricks. Used bricks are fine, best to have those all the same. Building with those is so much easier.

In the last week, Sabine and I have been thinking about the various options for positioning the batch box and the riser and have found a setup that meets most requirements, if it works.
It was an active process with a lot of thinking and trying out, encountering problems and finding solutions.
Then yesterday morning something happened that fascinates me over and over again, each time this happens.
Suddenly there is an idea, completely new, something we hadn't even thought of.
Apparently, our brain is working on its own plan in the background.

Setup Nr1 is the result of our active planning and testing.
Setup Nr2 the plan of the brain.
If you think that can work, we would prefer setup 2.

I hope that the drawings and the explanation are understandable

One more question.
Peter, you suggested in the first post that a 20cm riser could also work, but you said it would be an "overkill". What do you mean by "overkill"? What would be the advantages and what would be the disadvantages. If it's just a matter of "too much heat" being produced, that wouldn't be a problem for us and there's enough space with setup 2. We could also possibly plan an extension, with a sluice (which can be opened as needed) to a canal that leads outside into a future outdoor room.

As usual, I've attached a PDF with sketches and explanations.
We are now very curious about your answers.
Very best regards
Armin

Your concept #2 is cool, but it has one feature that will inhibit operation. The gases in the large stratification chamber will be cooling, and therefore becoming denser and wanting to sink. The outlet to the chimney needs to be close to the bottom of the chamber, and ideally the inlet from the other side would be closer to the top, or at least have a baffle to move incoming gases upward.

The short answer: in my view, it won't work. The longer answer is also complicated but I'll try.

Let's start with idea #1. As I see it, you are trying to make the smoke path longer in order to extract more heat. That's right opposite of the workings of a bell, plus you are situating it in an area where the temperature is already quite low. In the bottom of a bell there's not much heat to harvest. The point of a bell is slowing the gas velocity down very much, so there will be a longer stay which in turn promotes the extraction of heat.
Another pont is this: the batchrocket system is developed with bell technology in parallel, the system is very picky about friction in the smoke path. Bell systems are free flowing, heavily depending on buoyancy of gases. Given enough space, the gas velocity will go down to almost zero so gravity can do its work, keeping the hottest gases in the top and driving the coolest gases down to the exit. As such, it's a displacement system.

Now idea #2. Keeping the above in mind, this idea will be double or triple troublesome. You want here to lead the hottest gases down around the riser, send it in a horizontal channel, into a larger bell that's equipped with a vertical down channel where the exit isn't close to the floor. The net result is a system that has a lot of friction, probably won't come up to working temperature as well. Starting the thing will be a real problem, I dislike the idea of fighting with it every day. The kitchen side of the heater will get very hot and the small bell will eventually crack apart due to the stresses of the heat cycle. A bell is different, the produced heat is spread over a very large area, being the inner wall. A plus for urban areas: due to the low gas velocity, fine dust will be separated from the gas and will collecting on the floor of the bell. Provided the firebox is half a meter or more above it, so there's lots of space beneath it.

What you guys are doing is trying to use what you know about stoves. Sadly though, most of stove wisdom isn't a good fit for bell and batchrocket technology. The batchrocket is a quite extreme wood combustor, no other wood combustion systems burns as fast. Which means it produces an enormes amount of energy in a relative short amount of time. That's alright in a large brick bell, provided it's build the right way it is able to handle this.

Successful operating batchrockets are almost always coupled to bells. Personally, I know of just one that's besides three 200 liter barrels coupled to a piped bench of just one straight run and one elbow to vertical. All others are pure bells, nothing else.

As for the 200 mm system probably being overkill: it's a small house, a large system (believe me, a 200 mm one is!) occupies a lot more space than the 180 mm system. It might be that there's more space in the living room side than in the kitchen. Is it possible that the heater of roughly 90 by 90 cm footprint is better situated in the living room? Please keep in mind the old chimney construction will also function as warm mass when the bell is built against it.

Of course, you are entitled to build your own heater in the way you like it. It's your heater, your house. But it might be better to stay on the proven path and avoid untrodden territory.

Hello everyone!

@Phil Stevens thank you for your comment.
After that I tried to find a solution but then Peter's post came in with the nockout arguments...

"Starting the thing will be a real problem,..."
"The kitchen side of the heater will get very hot and the small bell will eventually crack apart..."

So the RMH will stays on the living room side.

Now a few questions about the position.
1) Is the position in #1 basically ok?
2) How much space does there need to be between the bell and batchbox and around the riser?
3) how much space must be above the riser to the bell. I read that at least 12" (approx 300mm? ) above the riser. What is the optimal distance?
4)  Must the heater/riser be built on level 2 at the same height as the hole in to the chimney, or can I build the heater/riser lower to around level 1?
     See attached pictures.
5) Is it better to use fireproof mortar or a fireproof “glue”, for heater/riser? Like this in the attached pictures.

Thank you for your patience and sorry if it takes me so long to understand.

Best regards, wherever you are!
Armin

Armin, I understand you want the footprint of the heater not to be larger than the space where the old stove has been. Of course you can do that but the core should be small as well, matching the bell space where it is in. Otherwise, with an oversized core, lots of precious heat is wasted through the chimney, effectively heating the birds. At the same time, you seem to be reluctant to demolish part of the old chimney construction.

Both the above targets can't be met at the same time, sorry to say. A mass heater will be much larger than the old stove ever was. The surface temperature of the mass heater will be much lower so in order to achieve the same heating capacity, the surface area need to be larger accordingly. The way you arranged the bricks in the pictures suggest you want to use the old chimney complex as the back wall of the bell. Please, please, don't do that. Due to temperature differences the heater will crack apart from the chimney, whatever you do, with leaks and stench in the house as the result.

Now the questions:
1) The level of the core isn't important, the position of the exhaust opening is. Relative to the floor of the bell, not relative to the core. Raising the bell in its entirety from the floor would mean it need to be wider and deeper in order to meet the core requirements.
2) Around the firebox there should be at least 5 times the cross setion area of the riser. Assuming the bell has vertical walls, around the riser there's much more space, only beneficial for extracting heat. The core doesn't need to be in the center of the bell, on one side is possible as long as it is separated from the bell's wall.
3) The absolute minimum space above the riser is the same dimension as the riser's diameter, preferably a bit more. There's no practical maximum, one meter would do as well. I would call about twice the riser's diameter probably the optimum distance when height constrains are a concern.
4) The level thing is probably because of the exhaust opening? The core doesn't need to be on the floor, a raised floor is not necessary for the workings of the bell. I'll do a proposal further down to solve the exhaust problem.
5) Fireproof (or refractory) mortar or glue for the core is right, thin seams of 1 or 2 mm are in order.

In order to get this project going, it is important to accept the size requirements of a mass heater. The difference between a stove and a mass heater could be decribed as follows:
The stove is small in summer, lots of people place a pot plant on top. In winter it is very large, everything that's combustible need to be at least a meter away from it, otherwise it will burst into flames in short order.
The mass heater is right the other way around, in summer it is very big and it stands in the way quite often. In winter it is small, stools are placed against it and people are competing with dogs and cats for the best places. The whole family lives literally against the warm walls.

My proposal: chisel away the bricks which are inside the old construction, below the lowest chimney opening. Build a surrounding around the chimney entrance so that there's a spaciously down channel, only the top and sides of it.
Now, build the entire bell in front of it, preferably wider than the chimney. The back wall of the bell against the chimney and against the down channel, with a spaciously opening at floor level.
I don't know the ceiling height, assuming it is about 2.5 m. The total height of the bell shouldn't be more than 2.3 m then. The inside height will be maximum 2.1 m in that case. Calculating a bell for an 18 cm system leads to roughly 7.5 m² inner surface area. Such a bell will be 90 cm wide and 70 cm deep in that case. The outside measurements, assuming the available bricks are 10 cm wide, would be 110 cm wide by 90 cm deep.

Such a heater will heat your small house quite comfortably, day and night, all through winter. Provided it will be fired once a day at least, not all day long and cold in the morning like a steel or iron stove.

It's up to you what to decide.

Uncle Mud's expertise may help. Here is a clip of the movie Freaky Cheap Heat, where he talks about the challenges of incorporating a rocket heater in a tiny house, underlining the need for heat storage to avoid abrupt temperature fluctuations.

Hello everyone!
Here is my new setup.
If everything is ok now, I can start building it.
Questions:
1) As you can see in the drawing, the maximum ceiling height is 2.3m.
    I would like to stay at least 200mm below the ceiling.
    This means for the height of the entire structure:
   - on the concrete floor a layer of bricks: 50mm
   - then a layer of refractory bricks as a floor for batch box/riser: 50mm
   - on it riser/batch box: 1300mm
   - cover of the Bell a total of 100mm??? : 100mm
     = 2300mm – 1500mm = 800mm remaining height for the distance between riser and bell ceiling.
   Did I forgot something?

2) The black area in the picture shows the part that I want to remove from the old structure. Down channel to the bottom.
    What diameter should the channel have?

3) P-Channel Dimensions. I'm having difficulty understanding the formula. What are the dimensions for
   this oven?
    Where should I position the P-Channel in this case? At the bottom of the batch box or at the top
    on it?

4)Ceramic fiber insulation mat. How thick?

Now all I have to do is wait for your GO!

Best regards to everyone out there!

Armin

Ceiling height 2300 mm, heater height 2100 mm, top deck roughly 100 mm. So internal height would be 2000 mm. Core height 1300 mm, so there's a top gap left (the space between riser and and ceiling of the bell) of 700 mm. In order to be able to load the heater easily, it would be best to raise the core in such a way the firebox' floor is 500 mm from the room floor. The top gap is thus reduced to 200 mm now, which is close to the minimum of 180 mm in your case, so this is OK.

My original calculation assumed an internal height of 2100 mm so you are losing some internal surface area now, from now I refer to that as ISA.
You could choose to build a pedestal of about 450 mm high out of bricks and place the core on top of that. By doing that, there's some ISA gained by the walls of the pedestal, and also quite some mass.
Although... for the proper working of the heater (starting cold for example) it would be better to have a space under the core that's completely empty. That could be achieved by utilizing three angled steel profiles, one that's resting on the bell bricks left and right of the firebox and two that are resting on the first one at the rear and on the bricks under the front of the firebox. This might sound complicated but be assured it isn't in reality.
Here's a picture of a similar setup, although the heater is entirely different.


And a drawing of what it looks like for you.


A comment about your setup: the front of the core should be flush with the front of the bell. Otherwise, a number of normal bricks would be inside the firebox. The firebox' top and sides need to be entirely separated from the bricks of the bell by means of a strip of superwool.

This is about it, if I see other things you need to know, I will post again.

Rereading, I saw an omission from my side. In order to be able to clean out the chimney, there should be a clean-out hatch in the bell and one in the chimney. For that last one, it would probably best to make a hole from the other side of the chimney. When the steel support is used, one hatch in the bell is sufficient. For the brick pedestal you need at least two, low in the bell and left and right of the core.

Just a thought: you could do three or four layers a day and take pictures of every layer. Post those in the evening and I will be able to comment, the same day most of the time.

Hello!

Thank you Peter for your offer to accompany the construction. I had already planned to document the work.
I hope to start demolishing the canal tomorrow and then I want to cut out the wooden floor.
I haven't bought the bricks for the bell yet because I'm hoping to get feedback from various friends by next week if they know anyone who has old bricks that are no longer needed.

In the meantime I have found out where I can get the Superwool.
There are different variants:
Superwool plus (Classification temperature: 1200°C. Maximum continuous application temperature: 1000°C. Tensile strength: 128 kg/m3 75 kPa) 2690 kr = 225€ = 240 USD

Superwool XTRA (Classification temperature: 1400°C. Maximum continuous application temperature: ? Tensile strength: 128 kg/m3 90 kPa) 3750 kr = 314 € = 335USD

The Superwool Plus in Sweden is ca. €90 cheaper than the Superwool XTRA and another €130 cheaper if i buy in Germany:
ca.122€ = 130USD  (Superwool Plus 25mm x 61mm x 7200mm) with shipping.

Is the Superwool Plus enough or do I need the Superwool XTRA?

To lay the bricks for the bell, do I use normal cement mortar?

Attached is a sketch with a first version of how I could imagine the steel beams.

Best regards wherever you are
Armin

Super wool needs to be treated with respect, look for body soluble version as they are safer to work with but still be aware of the facts of the individual product and use a mask.
Also be aware that once the material has been heated, it could be a serious heath hazard if it is disturbed and the fibres become airborne
There are alternatives but none are as effective or as easy to install.

Armin Speiser wrote:Is the Superwool Plus enough or do I need the Superwool XTRA?

Superwool plus is what you want. Use a mask, as Fox James already mentioned.

Armin Speiser wrote:To lay the bricks for the bell, do I use normal cement mortar?

Yes and no. The mortar is a mix of sand, lime and cement. Proportions for the mortar: 15 volume parts of sand, 4 parts lime, 2 parts portland cement. The cement is only there to allow you to go on with the build, without it you have to wait a couple of days after laying three layers.

Armin Speiser wrote:Attached is a sketch with a first version of how I could imagine the steel beams.

The T-beams in the ceiling the other way around, spanning the shortest distance.
I am in the dark about the welded beams in the top half of the drawing. What is it?

Sorry, I was probably a little too careless with the last drawing. This relates to your suggestion of placing the riser/batch box on beams. Since the beams are nearly 1,10 m long , I thought about supporting them with welded legs. But one in the middle of each beam would probably be enough. I hope the new drawing can clarify my thought.
Or do the legs interfere with air circulation?

Armin Speiser wrote:Sorry, I was probably a little too careless with the last drawing. This relates to your suggestion of placing the riser/batch box on beams. Since the beams are nearly 1,10 m long , I thought about supporting them with welded legs. But one in the middle of each beam would probably be enough. I hope the new drawing can clarify my thought.
Or do the legs interfere with air circulation?

Ahhh... I get it now. In case the two supporting beams are connected, this is a very stable construction. No interference with air circulation expected.

I'm really happy! The first step is taken!

Today we started the fun part of the project. After all the thinking and planning over the last few weeks, finally some real work! Dusty, dirty and at the end of the day I can see a result! I love it!

Thank you all for your patient support.
Best regards
Armin

Don't you forget to close up the holes that aren't to be used  with brickwork. And chiseling the hole for the cleaning hatch from the other side of the chimney leading to the lowest opening.

I am assuming you are planning to use the lowest opening, the channel leading up to this could be built together with the bell's wall in front of it. Expansion at that level won't be much and the construction would prevent developing long vertical cracks which potentially could leak.

Hello everyone.
If it is true that everything has its right moment, then it seems like this is not the right time for this project.
The last two weeks have been a roller coaster.
Joy and disillusionment are often close together.
Long story short, we had so many unforeseen expenses that even the small budget for the oven is gone and we can't buy the bricks for the bell at the moment.

If there's one thing I've learned in these first fifty years of my life, it's: "If there's a lack of flow in a project, you shouldn't try to force it, if possible."
So I have to put the project on hold for now and get the long underwear out of the closet.
Thank you for your support so far.
I'll be back as soon as the flow (and the money ) is back.

Wish you a nice autumn.
Wherever you are.
Armin

Hello everybody. I'm back again.
A little Christmas miracle.
We finally have the bricks for the stove and also someone to weld the substructure for the BatchBox/Riser.
So almost everything is ready.
While going through the plans and posts I realized that I'm missing the dimensions for the P-Channel.
I'm not sure if I understood the formula correctly.

P-channel dimensions
Width W = B/2 18cm/2=9cm
Height (thickness) = ((3.14(D/2)^2)*.05/W  
                                 ((3.14(18cm/2)^2)*.05/9cm=1,4cm
Is this correct?

Where should I place the P-channel in this case?
At the bottom of the batch box or at the top?

What is the difference, except that the top version is easier to build?

If nothing else comes up, I plan to start building the first or second week of January.

I wish you all a very Merry Christmas full of love, joy and warmth!
Wherever you are!
Armin and Sabine

Happy Christmas Armin, I think you can find all the dimensions on Peters site https://batchrocket.eu/en/building
Yes easier to replace on the bottom …..

Armin Speiser wrote:Where should I place the P-channel in this case?
At the bottom of the batch box or at the top?

The p-channel is the overhead secondary air channel. So this should always be on top, no other choice. The floor channel is always on the ehrm.. floor and in general both are delivering fresh air at the top half of the port.

Armin Speiser wrote:What is the difference, except that the top version is easier to build?

The difference is the placement and the way the air is fed in. The p-channel is built in, not easy to replace. It has its own supply from outside the firebox and in that respect requires a separate valve to close it. The whole of the channel is 5% of chimney's csa.

The floor channel is the more advanced of the two, laying in its own trench. The horizontal part, called feed, is twice as wide csa-wise as the vertical part, the stub. By constructing it like this, the air speed in the stub will be quite high because of the temporary nature of this orifice. Due to the higher air speed the cooling of this part is therefore much better. The stub's inside is 5% of the chimney's csa.

The best construction is to have this floor channel starting just behind the door, about 4-5 cm distance. On top of the start end also a steel strip of say, 6 or 8 cm high, which keeps the ash inside. So there's a free space of 4 cm behind the door where the feed starts, and in order to reach the fuel pile the air need to go up. It keeps the glass clean this way, but that's a secondary function. In fact, the air inlet need to be right in front of the floor channel. The primary air need to go up in two bends of 90 degrees and the floor channel is fed straight at all times. During the burn the emphasys is shifting from primary to secondary air this way, exactly what is required, because in full burn there should be more secondary air supply. As such, this is an automatic system.
Quite some explanation now I reread it, hope this is clear though.

Armin, I know nothing about the technical aspects of any of this, but just want to say how glad i am that things unfolded for you so you can go ahead with this project. Miracles do happen!

Thank you both for the prompt reply and, dear Peter, for the detailed explanation! I will now try to understand it and probably come back with more questions.
For today, I wish you a joyful Christmas Day.
Armin

Thank you for your thoughts, dear Jane!
Just to say: "I have no knowledge to share with you, but my heart is with you" is wonderful and gives strength and joy. It is this way of thinking and empathizing that makes this community so special.
A magical Christmas to you too.
Armin