Flue pipe diameter

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.

Hi Mathias.
As far as I know you can get away with using a bigger diameter in the direction of the flow. But a smaller is usually not a good idea.
Also 3 90 degree elbows seems like a lot. Any way you can simplify that?
But I’m also not a BBR expert. So maybe it’s an option.
When you say stove you mean an actual cooking stove or a heater to keep your house warm?

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!

Hi Matthias;
I agree with Ben, you need a matching chimney, perhaps even a 150mm for your 5.1" Shorty.
I have both a Shorty and several 1st-generation Batchboxes.
Shorty is an incredible stove, but she does not have the power of a first-gen.
As casual as Shorty burns, she "might" flow with a smaller flue, but there is a much better chance she will not like it.
Peter has recommended the use of a bypass with Shorty, something he did  not recommend with his other designs.

You could try if you wish, but I would have a larger pipe on hand; I think you will need it.
Perhaps Peter will give us his opinion.

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!

You can build a sidewinder with the port and riser on one side of the firebox, if you are not restricted on bell width.