My first Batchbox build, on top of Barcelona's mountain.

Best to shape it with cob and lots of straw. Th render is just for looks then.

That's convenient because we can use this extra thickness to try and make the bench a bit more comfortable. A 90º angle seat it's not good for the back.


I've finally managed to draw something that makes sense with sketchup.

Firebrick - 230x114x64 mm

IFB - 230x114x64 & 230x114x30 mm

I'm I going in the right direction? Are there any crucial mistakes?  

sara ventura wrote:I've finally managed to draw something that makes sense with sketchup.

Firebrick - 230x114x64 mm

IFB - 230x114x64 & 230x114x30 mm

I'm I going in the right direction? Are there any crucial mistakes?  

Yes, this is right direction and yes, there are some crucial mistakes.
Namely: the liner opposite the port shouldn't be there, the top half of the riser box should be square, sides equal to 2B.

Your bricks are slightly larger than usual, not easy to adhere to the correct proportions if figure B is exactly 72.34% of the diameter of the chimney. What I usually do with this size (150 mm) of core is this: I'll take the width of the bricks, in your case 114 mm, and use that as the Base figure.

Don't worry too much about it, I'll draw you a core that is the right size and proportions, based on the bricks that are available to you.
Could take some time to find a couple of hours that aren't filled in already. I'll try to have it completed before the end of the week.

What I usually do with this size (150 mm) of core is this: I'll take the width of the bricks, in your case 114 mm, and use that as the Base figure.

Don't worry too much about it, I'll draw you a core that is the right size and proportions, based on the bricks that are available to you.  

Thanks Peter, that's so generous! and life-saving, I've tried to do the math with Base figure, but my brain switches off at some point and I get lost. 😅
No rush at all. From my drawing, I can do an overall estimation of the bricks I need already.

I've read somewhere that a 20% increase is the usual to add to the amount needed of bricks, is that correct?

Also, I've realized while drawing I forgot there are 2 types of brick, not sure that I can lay both between them as I've done? Different expansion rates, perhaps?

Yes, this is right direction and yes, there are some crucial mistakes.
Namely: the liner opposite the port shouldn't be there, the top half of the riser box should be square, sides equal to 2B.

No wonder, I was trying to copy from the .skp Sidewinder shorty from your site combined with the dimensions from the shorty chart, but doing the riser I felt a bit lost. Never used sketchup before.


I've drawn the top's firebox using the refractory slab G-23, which leaves three joints on the top. Would it be better to have a single piece instead?

And the single piece that doubles as top exit riser's port and base of the riser's top, should be from the same material as the rest of the riser? Can I use a cut from the G-23 slab?

thanks for your guidance!

sara ventura wrote:I've read somewhere that a 20% increase is the usual to add to the amount needed of bricks, is that correct?

That could be correct, or not, depending on what you are building. Better to count the bricks individually when the drawing is finalized.

sara ventura wrote:Also, I've realized while drawing I forgot there are 2 types of brick, not sure that I can lay both between them as I've done? Different expansion rates, perhaps?

I am unsure what type of insulating firebricks you have there. Better to use just hard firebricks for the entire core. The riser is the part that's heat stressed most of all, especially the liner in the lower half. Thin strips of insulating firebrick, I feel scary about its durability.

sara ventura wrote:I've drawn the top's firebox using the refractory slab G-23, which leaves three joints on the top. Would it be better to have a single piece instead?

Not necessarily, it could be done in two pieces as well, three is also possible.

sara ventura wrote:And the single piece that doubles as top exit riser's port and base of the riser's top, should be from the same material as the rest of the riser? Can I use a cut from the G-23 slab?

Yes, you can, no problem.
I"ve had a look at your drawing of the core, and question arose. The depth of the firebox, is that a fixed figure because of the bell depth?

I am unsure what type of insulating firebricks you have there. Better to use just hard firebricks for the entire core. The riser is the part that's heat stressed most of all, especially the liner in the lower half. Thin strips of insulating firebrick, I feel scary about its durability.

I have located a high temp materials factory that offers:

Insulating firebrick G-26 -
Dimensions: 230 x 114 x 64 mm
Maximum temperature: 1430ºC
Alumina: 56%
Characteristics:
Excellent insulating qualities.
Mechanical and temperature resistance superior to group 23 bricks.
High purity.
Thermal shock resistance.

Firebrick AL40-
Dimensions: 230 x 114 x 64 / 76 / 20 / 30 / 40 mm
Maximum temperature: 1420ºC
Alumina: 39-41%
Characteristics:
High purity.
Low iron content.
Good mechanical resistance.
Excellent resistance to thermal shock.

I'm trying to avoid ceramic wool as much as possible, I was going with the insulated firebrick for the riser, so I don't have to add extra insulation outside. Keeping the ceramic blanket at minimum when directly exposed to gases.

I"ve had a look at your drawing of the core, and question arose. The depth of the firebox, is that a fixed figure because of the bell depth?

I've drawn 50 cm because the depth is the lenght that has more tolerance, and I'm thinking in the type of wood I'll be using.
Most of the times the horitzontal cuts of the wood are at an angle, length is always irregular. So extra depth to make sure I can fit any kind of cuts in the box load.

sara ventura wrote:I'm trying to avoid ceramic wool as much as possible, I was going with the insulated firebrick for the riser, so I don't have to add extra insulation outside. Keeping the ceramic blanket at minimum when directly exposed to gases.

In that case, I've got news for you. This core type can do very nicely without insulation at all.

That's good news, indeed! IFB are 1€ plus per piece than Firebrick😅

Peter van den Berg wrote:This core type can do very nicely without insulation at all.

Maybe I should explain a bit what happens inside this Shorty core.
In order to obtain complete combustion or close to this state of affairs, the three T's are important. In no particular order: temperature, turbulence and time. Some mainstream knowledge say smoke should disappear as soon as a temperature of 850 ºC (1560 ºF) is reached. There's even a German group by the name of 850 Grad, which is promoting this idea. Of course, nobody specified where that temperature should be reached and accompanied by which amount of turbulence and during which amount of time. Since I've seen numerous times smoke disappearing within 5 to 10 minutes into a burn after a cold start, I started wondering. The numbers doesn't look like fixed figures, it could be that the figures are at least partly interchangable. Maybe, with an awful lot of turbulence induced both the other two T's, time and temperature, could be smaller.

Actually, I am convinced this could be the case, although I am unable to prove it. A young master heater builder from Germany visited me last year, and he was very surprised my Testo gas analizer showed such low CO numbers after 5 minutes into the burn of a cold Pepper Shaker heater. At the same time, the temperature in the afterburner area couldn't have reached at least 850 degrees C, far from it.
Interesting line of thought, don't you think?

sara ventura wrote:That's good news, indeed! IFB are 1€ plus per piece than Firebrick😅

Using hard firebricks seems to be the logical way to go, then.

Peter van den Berg wrote:The numbers doesn't look like fixed figures, it could be that the figures are at least partly interchangable. Maybe, with an awful lot of turbulence induced both the other two T's, time and temperature, could be smaller.

Actually, I am convinced this could be the case, although I am unable to prove it.

I was under the impression that a person could cheat and use a fan and/or a heater to decrease the amount of time before a smokeless fire is achieved.
If so, wouldn't using such devices be able to prove that these numbers are not fixed but are interchangable as you mention?

OK, the drawing is ready. I couldn't find a good example of the door assembly, I will look for it. The whole of the core is a little bit larger, although it will run without any problem on a 150 mm chimney diameter.

Gerry Parent wrote:I was under the impression that a person could cheat and use a fan and/or a heater to decrease the amount of time before a smokeless fire is achieved.
If so, wouldn't using such devices be able to prove that these numbers are not fixed but are interchangable as you mention?

I am inclined to say you are right, good thinking. But the combustion system would change from an atmospheric aspirated device (is that the right term?) to a blown combustion system, like a wood gasifier. Food for thought, no doubt about it.

sara ventura wrote:

I am unsure what type of insulating firebricks you have there. Better to use just hard firebricks for the entire core. The riser is the part that's heat stressed most of all, especially the liner in the lower half. Thin strips of insulating firebrick, I feel scary about its durability.

I have located a high temp materials factory that offers:

Insulating firebrick G-26 -
Dimensions: 230 x 114 x 64 mm
Maximum temperature: 1430ºC
Alumina: 56%
Characteristics:
Excellent insulating qualities.
Mechanical and temperature resistance superior to group 23 bricks.
High purity.
Thermal shock resistance.

Firebrick AL40-
Dimensions: 230 x 114 x 64 / 76 / 20 / 30 / 40 mm
Maximum temperature: 1420ºC
Alumina: 39-41%
Characteristics:
High purity.
Low iron content.
Good mechanical resistance.
Excellent resistance to thermal shock.

I'm trying to avoid ceramic wool as much as possible, I was going with the insulated firebrick for the riser, so I don't have to add extra insulation outside. Keeping the ceramic blanket at minimum when directly exposed to gases.

I"ve had a look at your drawing of the core, and question arose. The depth of the firebox, is that a fixed figure because of the bell depth?

I've drawn 50 cm because the depth is the lenght that has more tolerance, and I'm thinking in the type of wood I'll be using.
Most of the times the horitzontal cuts of the wood are at an angle, length is always irregular. So extra depth to make sure I can fit any kind of cuts in the box load.

I know things are different around the world but when I ever hear about insulating fire brick being lighter and ect. I have to let folks know.  As many have read, about my 7" batch box,  it has worked just fantastic, And because of the tremendous draft, can get to perhaps hotter than most. On the third the burn.

But I am hear to say, I used what I thought was the best "insulating fire brick" I could get my hands on in the states. And after a few years these have started to break down, while the hard fire brick has NOT SHOWN any problems. (same stove)  This was not caused by thermoshock, abrasion from fire wood, nor anything else I can think of.   and Simply used in the riser.  Not the end of the world by any means, but still some maintaince that I was not planning on doing this summer.  This is no fault of the design, simply these bricks could not handle what I was asking of them.

Am pretty sure if I had done the exact same thing with hard fire brick, with wrapped insulation, I would still be 100% good.

Again, results may very, but this is just my case as stated.

cheers
Scott

Thanks Peter for the drawing! I'm crunching numbers for the bell again since I realized I was leaving out the top of the bell in my previous calculations...

As it is now, I'm at 6m2 ISA and I need to reduce it a little. Quick questions about internal dimensions :

-Space between riser's top and bell's top  ---> I have now 30 cm, could it be reduced to 20cm?

-Lowering the core 5cm ---> Core 5 cm lower than the bench's top, but still 25 cm above the floor, is it feasible? Would it compromise the gases flow too much?

-Bench height and width ---> Height is now at 30 cm, I can't go lower. Width is at 60 cm, could I make it 50 cm and add this in mass to the exterior to keep 60 cm depth for the bench seat? It could be done either with brick or cob this extra thickness outside? I assume this would lower also the temp of the wall outside, but the idea of keeping the calfs fresher than the rest of the body sounds good to me.

If I can combine these three changes I could lower the ISA to 5'56.

   Peter van den Berg wrote:
   This core type can do very nicely without insulation at all.


Maybe I should explain a bit what happens inside this Shorty core.
In order to obtain complete combustion or close to this state of affairs, the three T's are important. In no particular order: temperature, turbulence and time. Some mainstream knowledge say smoke should disappear as soon as a temperature of 850 ºC (1560 ºF) is reached. There's even a German group by the name of 850 Grad, which is promoting this idea. Of course, nobody specified where that temperature should be reached and accompanied by which amount of turbulence and during which amount of time. Since I've seen numerous times smoke disappearing within 5 to 10 minutes into a burn after a cold start, I started wondering. The numbers doesn't look like fixed figures, it could be that the figures are at least partly interchangeable. Maybe, with an awful lot of turbulence induced both the other two T's, time and temperature, could be smaller.

I get lost with the specifics of the science, but I get the general idea.
So I could go for a core made all from firebrick, without covering it with ceramic blanket to keep the maximum heat in, and still have a clean combustion that guarantees the optimal functioning of the heater.

I used what I thought was the best "insulating fire brick" I could get my hands on in the states. And after a few years these have started to break down, while the hard fire brick has NOT SHOWN any problems. (same stove)

Thanks Scott for your input. It's actually helpful because the main reason I was going with IFB was longevity, the not needing extra insulation outside was a bonus (for me).
And considering IFB are the most expensive type of brick from the three I was sourcing for the build, it's a great experience to hear.

I keep drawing the bell, let's see if I can come up with a functioning bench in the end.

Thanks for all your time and experience!

Scott Weinberg wrote:But I am hear to say, I used what I thought was the best "insulating fire brick" I could get my hands on in the states. And after a few years these have started to break down

Scott, do you remember what brand and model of IFB you have used?
The insulating bricks in my gas kiln do not show any wear, but at the same time I use it sporadically, but at higher temperatures. I always inquire if IFBs that I purchase can work in flame path.

Cristobal Cristo wrote:

Scott Weinberg wrote:[But I am hear to say, I used what I thought was the best "insulating fire brick" I could get my hands on in the states. And after a few years these have started to break down

Scott, do you remember what brand and model of IFB you have used?
The insulating bricks in my gas kiln do not show any wear, but at the same time I use it sporadically, but at higher temperatures. I always inquire if IFBs that I purchase can work in flame path.

Simon fire insulated fire brick, nearly white in color ( not that makes any difference)  Again I am not blaming the brick, and perhaps this is a one case deal, I could get the exact details, but have decided in my case, it will be hard-high rated fire brick only. As all of those have survived very well.

I will check to see if they had a fire temp rating later today.

Scott

I have checked Simond's website. It looks that they just import their products from somewhere, otherwise they would brag about "made in USA". Asian manufacturers do have technology, but in case of making products for some reselling brands, the quality control may be absent. I have purchased some old new insulating bricks made by reputable Caldersys (created as a merger of US 100 year old Pilbrico and 200 year old French Lafarge). They are rated to 1350 C (2500 F) and are 3" thick. They were made in India. I needed to make some custom kiln posts. When I sliced 2 bricks I was amazed to find, that one of them had a 10 mm wide cavity inside with radiating cracks. I did not cut more, because I made enough posts from two bricks, but so far I can assume that 50% are faulty.
When I was cutting IFB23 made by Harbison Walker in China, every cut brick was perfect and uniform inside and I cut 8 of them.
It's the best to buy at local refractory dealers, they will have US made materials at online Asian prices.
Fire rating will not matter much if the product is not properly made
At the end I have to admit that I agree with Scott's philosophy and I also prefer stronger materials when building anything, even at a cost of reduced performance since longevity is most important aspect for me.

sara ventura wrote:As it is now, I'm at 6m2 ISA and I need to reduce it a little.

The accepted bell size for a 150 mm first generation batchrocket is 5.3 m². However, the top combustion rate of a Shorty core is somewhat tuned down, in order to create a much more reliable core. So, for a 150 mm Shorty, that ISA should be 15% less, being 4.5 m².
However... you could have an oversized bell ISA although a bypass is a must in that case.
Don't worry, please read on.

sara ventura wrote:-Space between riser's top and bell's top  ---> I have now 30 cm, could it be reduced to 20cm?

Top gap could be zero, but for safeties' sake, let's say 10 cm or 4" would be sufficient.

sara ventura wrote:-Lowering the core 5cm ---> Core 5 cm lower than the bench's top, but still 25 cm above the floor, is it feasible? Would it compromise the gases flow too much?

Better to have the core not lower than the bench, also construction would be much more logical.

sara ventura wrote:-Bench height and width ---> Height is now at 30 cm, I can't go lower. Width is at 60 cm, could I make it 50 cm and add this in mass to the exterior to keep 60 cm depth for the bench seat? It could be done either with brick or cob this extra thickness outside? I assume this would lower also the temp of the wall outside, but the idea of keeping the calfs fresher than the rest of the body sounds good to me.

The slabs for the bench could be 60 cm, sticking out on the outer side. Internally, the bench could then be 50 cm or even less. Making the wall of the bench beefier won't help much, the seat will be the warmest anyway.

sara ventura wrote:So I could go for a core made all from firebrick, without covering it with ceramic blanket to keep the maximum heat in, and still have a clean combustion that guarantees the optimal functioning of the heater.

Correct.

I am unsure whether or not I mentioned this, but there shouldn't be a wall between the main bell and the bench at all, just a few columns. Try to view the whole of it as a strangely shaped bell. Those columns are there for to support the slabs of the bench' seat, while at the same time the wall of the bell above the bench is resting on the slabs. For how to construct this, see my article about the French Bench.

I am unsure whether or not I mentioned this, but there shouldn't be a wall between the main bell and the bench at all, just a few columns. Try to view the whole of it as a strangely shaped bell.

You mentioned it here earlier, but it's a good thing to keep in mind.
I imagine the inside of the built like the inside of a big cavern in the dark, a large open floor plan and a ceiling at different levels.
In my case there will be a masonry column to divide the 90cm span of the bench and support the bell's wall, and 5 thin metal legs to rise the core.

The accepted bell size for a 150 mm first generation batchrocket is 5.3 m². However, the top combustion rate of a Shorty core is somewhat tuned down, in order to create a much more reliable core. So, for a 150 mm Shorty, that ISA should be 15% less, being 4.5 m².
However... you could have an oversized bell ISA although a bypass is a must in that case.

The bybass was already in my to do list. How much below the exit riser's port should it be placed? Should the opening of the bypass be facing the floor or the wall?

   sara ventura wrote:
   -Space between riser's top and bell's top  ---> I have now 30 cm, could it be reduced to 20cm?


Top gap could be zero, but for safeties' sake, let's say 10 cm or 4" would be sufficient.

That's good news! I can squash 20 cm from the top, leave the core aligned with the bench top and lower my ISA to 5'2.
Will I get away with that ISA and the bypass?

I also like the idea of the overhang of the bench slab, it gives the bench a more comfortable seat if you can bring your heels at a closed angle than 90 degrees from the knees.

So I can move ahead with my plans, will have something drawn this week and keep breaking the building details of the bell as I come across new doubts.

Thank you!

sara ventura wrote:The bybass was already in my to do list. How much below the exit riser's port should it be placed? Should the opening of the bypass be facing the floor or the wall?

What you wrote there is confusing me. Somehow, I get the impression that you think a bypass is a valve in the core itself. Just to be sure: it isn't, it's an extra opening between the bell and the chimney. Opening the valve in that opening is bypassing part of the bell, so that the chimney heats up much quicker. So, the position of the bypass could be halfway the height of the bell or somewhat higher.
The opening should face the core or the wall.

sara ventura wrote:I can squash 20 cm from the top, leave the core aligned with the bench top and lower my ISA to 5'2.
Will I get away with that ISA and the bypass?

Hard to tell, as long as the chimney is of good quality, it might, since the ISA oversize is now roughly 15%.

How much below the exit riser's port should it be placed? Should the opening of the bypass be facing the floor or the wall?

I used the riser's exit port as reference as I imagine the bypass is best placed close to it, so the hot gases find an exit before going down to the floor and bench.
I know the bypass is placed in the exit pipe, and the shape is a T section, in my case I'll use a butterfly flap that will be operated through the bell's top.

   sara ventura wrote:
   I can squash 20 cm from the top, leave the core aligned with the bench top and lower my ISA to 5'2.
   Will I get away with that ISA and the bypass?


Hard to tell, as long as the chimney is of good quality, it might, since the ISA oversize is now roughly 15%.

From the lowest point of the exit flue to the exterior top: 5 meters with 1 35º turn exiting the bell and another to enter the masonry chimney that the pipe will go through up to  the exterior. Pipe will be double walled.

sara ventura wrote:I used the riser's exit port as reference as I imagine the bypass is best placed close to it, so the hot gases find an exit before going down to the floor and bench. I know the bypass is placed in the exit pipe, and the shape is a T section, in my case I'll use a butterfly flap that will be operated through the bell's top.

Ahhh... I get it now. The intake end of the T to the side, away from the core. Height placement in your case, about the level of the firebox' deck. In other words, somewhat lower than the core's exit opening.

sara ventura wrote:From the lowest point of the exit flue to the exterior top: 5 meters with 1 35º turn exiting the bell and another to enter the masonry chimney that the pipe will go through up to  the exterior. Pipe will be double walled.

OK, although the bell is oversized for a Shorty core, you can get away with it since you've got an adequate chimney and a bypass. Chances are that you have to run the heater with the bypass open a crack permanently, especially during fall and spring. As long as the build is neatly done, it'll work as it should.