Batch box material feedback

Hi again!

I would highly appreciate comments on my choice of materials for an 8 inch batch box rocket stove... Also, if you have any suggestions as to how thick the different layers need to be... The temperatures listed are the max temps provided by the manufacturers when I purchased the materials. Teh burn chamber to the left and riser to the right (+ view from above).



Thanks!
Henric

Hi Henric;
I suggest putting 1 inch of ceramic blanket between the firebrick and clay brick.
Two reasons, first and most important you want your box to stay very hot.
Second, quite a bit of heat will transfer from the firebrick to clay brick and then into your metal skin, better to limit that transfer.

Next your vermiculite boards up the riser, I suggest staying with the 1500C all the way to the top.
An 8" batch, as Peter has stated is "A Beast!" I have a 7", and let me tell you it screams at full burn.
I have a cast iron roof in that batch and it is starting to sag a bit! That places temps over 1800F while still in the box...
Temps start to increase dramatically after passing thru the port and starting up the riser.

Thanks Thomas!

Do I need the 2 inch firebricks or is it enough with 1.. ? I have a lot of the latter.

Cheers,
Henric

Yes, the full-thickness bricks are more stable and do not crack as easily as the split bricks do.

I'll second Thomas in this. In addition, you have drawn the proportions not quite to the recommendations. Also, the riser as a rectangle might turn out a fundamental mistake. Of course you are obliged to do what you fit best, just be a warned man.

Thanks!

One last thing... if my existing chimney is a 6 inch pipe, does that restrict the rocket stove to max 6 inch?

Cheers,
Henric

Haha... it's a compliment you consider it a drawing 🙂 I use PowerPoint and I'm happy if you understand what it is.

Henric Togereux wrote:One last thing... if my existing chimney is a 6 inch pipe, does that restrict the rocket stove to max 6 inch?

That's true, some people got away with a 5" chimney on a 6" system. But that chimney was a round, smooth inside, insulated, straight up channel. In case you have such an ideal chimney, the scale of the core could be up a bit, let's say 6.5"?

Thanks Peter.

Too bad... there goes my 8 inch plans :/ I have a straight smooth pipe, but it's probably somewhere between 5 and 6 inches. Nowhere near 8. Installing a new one is a very expensive endeavor and would probably take a year of Swedish bureaucracy...

Cheers,
Henrik

My concern would be the expanding and contracting of the different materials. Especially where the normal brick is touching the old wood stove steel. I would think an expansion gap would help with this. Maybe cardboard which would burn out. Even though I do not know what this is going into. I find it a bitch to only have 1 access point into the stove. Again maybe you can build the stove from the top.... I am not sure.  

I have been redesigning the firebox in our cast iron stove and its annoying having to reach in from the door. I would love to be able to remove the top!

Thanks Jordan.

I'm still on the drawing board, so I will consider your thoughts 🙂

Regarding the size of an existing chimney and the max size of a rocket stove, does it matter that my existing flu ia over 12 m high, straight up and insulated? It has a very strong draft.

Cheers,
Henrik