Matthias Hacker

Imagine the bell as a cube of 1x1x1 meters. The ISA simply would be all (inner) surface areas minus the floor. So in case of the cube 6 minus 1 equals 5.

For loading the core with wood it is much more comfortable to have the core a bit higher in the bell. About half a meter above the floor is a good hight.

When you think about the size of the core, I‘d say bigger is better, because it needs less firing. In other words, with a big core you might be fine with one fire per day, while a smaller core will ask for two fires per day, to keep your house warm.

On the batchrocket site you will find a way to calculate the energy consumption of your house and which core size will fit.

But the limiting factor is the chimney diameter. The core size may not be larger than the chimney diameter.

Another factor is the floor construction, how much weight can it carry?

I’d also advise to build a simpel bell without a bench. And take a look at the shorty core!

Do some maths first, you have to know for example about base number and ISA of the bell. Then when you have decided in which ballpark you want to have your core, take a look at the refractory available to you. It makes the build much easier when you choose a core size, that asks for only some few refractory cutting. The less cutting the better!

Hello,

maybe of interest for those who want to add mass to a barrel. I recently made my own clay bricks with success. Working with clay is a nice thing in general. It´s an excellent heat storage!

I did use pure clay, I only added some dry sand in case my clay had too much water. The clay should be stiff, so that it remains it´s shape. I applied some oil to the template like you would do with a cake pan.

Best, Matthias

Hello everbody,

some questions came to my mind while making plans for my upcoming Shorty build. I hope it´s fine to ask them here. I searched the forum but didn´t find these questions asked.

- The V-shaped floor, is it essential? Coaling down is faster with the V-shaped floor, as I understood, right? Since I am planning to build a small core due to size restrictions, this floor design would make the burn chamber even smaller. And I don´t like to cut refractory too much...

- How do you guys take out the ash out without pushing it into the port of the burn chamber?

- Is the Shorty core prone to smoking back into the living room? If so, might a bypass higher in the bell (above the endport) help?


I have refractory slabs available of 250x120mm and 300x150mm and I found out, that a small 131mm system size core can be build with very few cuttings using this dimensions. Looking forward to start my build soon.

Thanks, Mat

Maybe of interest for those who want to build something similar, this is my small rmh wich i build last winter.

The core is a DSR3, it has in internal flue gas channel from where the pipe exit is visible down to the bottom, with a flap on top of the channel as as a bypass.

These barrels are made for shipping foods like peanut butter. I welded one lid to the bottom of the upper barrel, and later cut a large opening into as well the lid and the bottom of the upper barrel. That makes a perfect tight fit for stacking one barrel onto the other.

Now I’d like to build something similar, but with a shorty core and a t-style bypass on the outside, similar to Peters heater. And an easier way of dry stacking bricks inside came to my mind. My goal is to be able to build a transportable heater within a few days at low costs.

Another question came up, I’m still thinking about numbers and size…

Is it possible to build a shorty core a bit shorter (in length/depth) than specs? I am now leaning towards a 140mm (5.5 inch) core size, wich is my chimney diameter, but there is a restriction in total depth of the core, at least in the way I want to build the bell. Base number would be around 100mm,  so 4xB for the depth of the burn chamber would be 40cm, but I don’t need it to be deeper than 33cm.

Thank you guys!

Thank you Benjamin,

so I will look for a flue pipe that has at least system size. Not that easy to find here where I am, but will be possible.

Sorry stove is not the right term, I mean heater.

Liebe Grüße aus Serbien!

Hello to all of you

I’m thinking about building another small batch box rocket stove. Last year I finished a DSR3 and am really happy with it, but the idea of building another one with a shorty core keeps spinning in my head…

So a questions came to my mind
can I make the connection of a 130mm (5,1 inch) shorty core to the chimney with a 120mm (4,7 inch) flue pipe? The total length of the flue pipe might be around one meter, with three 90 degree pieces in it.

I guess this is not a good idea, but I like to know about your opinions first.

Matthias Hacker wrote:

After the heating season I will take everything a part and see what the stripes look like. I don‘t expect them to dissolve by the time, they are not directly exposed to heat and oxygen. If they are getting softer during the hottest burn, that wouldn’t be in issue, because they are  not structurally stressed.

I promised to make pictures of my stripes of stainless steel, so here they are. What do you think about it? I am not concerned. I could take my core apart and put it back together like a puzzle without any problems.

Nancy Reading wrote:Do you find the knob is getting hot? I Think that the wooden knob (although it looks nice) might not be durable.

Hello Nancy,
I‘m happy you like it!
the wooden knob is a getting a bit warm, but far away from getting hot.