Feed tube burn tunnel heat riser ratio.

Hello,
I'm looking for some solid advice on what's the best ratio for the feed tube to burn tunnel to heat riser for a j style rocket stove. I built my first one recently and it worked well but I felt like it could "rocket" even better. I think I made the burn tunnel too long, like I said I still got some good rocket action but I've had conflicting advice on how to figure out my measurements. Any help would be appreciated, thanks.

Hi Joe;
On an 8"  J tube.
Your square openings must be 7.5"x7.5"
The height of the feed tube should be 16" deep.
The burn tunnel should have no more than five bricks on the edge or no more than a 12.5" roof.
The riser should be no less than 40" + tall

On a 6" J tube the square openings should be 5.5"x5.5"

thomas rubino wrote:Hi Joe;
On an 8"  J tube.
Your square openings must be 7.5"x7.5"
The height of the feed tube should be 16" deep.
The burn tunnel should have no more than five bricks on the edge or no more than a 12.5" roof.
The riser should be no less than 40" + tall

On a 6" J tube the square openings should be 5.5"x5.5"

Thanks thomas this is helpful. I'm kind of looking for a formula. I'm doing unconventional stuff with uncunconventional materials. I've heard 1 2 4, 1 3 4, 1 1.5 4 for length ratios and I've also heard that it's more of a volume thing. You seem to be very experienced and I am not so maybe I'm wrong and there isn't exactly a ratio formula I can use.
Thanks again for the response.

Joe Schuler wrote:

thomas rubino wrote:Hi Joe;
On an 8"  J tube.
Your square openings must be 7.5"x7.5"
The height of the feed tube should be 16" deep.
The burn tunnel should have no more than five bricks on the edge or no more than a 12.5" roof.
The riser should be no less than 40" + tall

On a 6" J tube the square openings should be 5.5"x5.5"

Thanks thomas this is helpful. I'm kind of looking for a formula. I'm doing unconventional stuff with uncunconventional materials. I've heard 1 2 4, 1 3 4, 1 1.5 4 for length ratios and I've also heard that it's more of a volume thing. You seem to be very experienced and I am not so maybe I'm wrong and there isn't exactly a ratio formula I can use.
Thanks again for the response.

Ok, I just reread what you wrote and understood it this time. I think I can get the ratio I'm looking for from what you said. Thanks.

Good morning Joe;
I'm not much of a math person. But I have built many RMHs
I also have heard the ratios you mentioned.  They never made much sense to me. A tape measure reads inches, not ratios.
The measurements I gave you are the official numbers.
If you are good with math you might be able to convert them to a ratio.

I built with a too-long burn tunnel one time.
Worked seemingly great until mid-winter when my rocket started sounding like a bottle rocket and then progressed to wanting to smoke back.
An inspection found I had been producing way too much ash and my horizontal pipes were 80% full!
I did a rebuild in the middle of the winter that year...  not recommended.

A ratio I like is 1:1.5:3, measured along either the centerline or the outside edge of the space. That can give an 8" J-tube with 16" feed (fits standard firewood), 24" burn tunnel floor and 8"+ ceiling, and 48" riser.

You could make a 6" J-tube with the same figures; it would look more stretched out, but would still hold standard firewood. This matters because you really want your wood to fit completely within the feed so you can cover it quickly in case of any emergency, or just as part of normal operation - I find mine operates best with the feed around 3/4 covered, don't need as much air as flows through an unrestricted opening.

thomas rubino wrote:Good morning Joe;
I'm not much of a math person. But I have built many RMHs
I also have heard the ratios you mentioned.  They never made much sense to me. A tape measure reads inches, not ratios.
The measurements I gave you are the official numbers.
If you are good with math you might be able to convert them to a ratio.

I built with a too-long burn tunnel one time.
Worked seemingly great until mid-winter when my rocket started sounding like a bottle rocket and then progressed to wanting to smoke back.
An inspection found I had been producing way too much ash and my horizontal pipes were 80% full!
I did a rebuild in the middle of the winter that year...  not recommended.

That's great very helpful thank you vary much for your help.

Joe Schuler wrote:

thomas rubino wrote:Good morning Joe;
I'm not much of a math person. But I have built many RMHs
I also have heard the ratios you mentioned.  They never made much sense to me. A tape measure reads inches, not ratios.
The measurements I gave you are the official numbers.
If you are good with math you might be able to convert them to a ratio.

I built with a too-long burn tunnel one time.
Worked seemingly great until mid-winter when my rocket started sounding like a bottle rocket and then progressed to wanting to smoke back.
An inspection found I had been producing way too much ash and my horizontal pipes were 80% full!
I did a rebuild in the middle of the winter that year...  not recommended.

That's great very helpful thank you vary much for your help.

Thanks that sounds great.

Glenn Herbert wrote:A ratio I like is 1:1.5:3, measured along either the centerline or the outside edge of the space. That can give an 8" J-tube with 16" feed (fits standard firewood), 24" burn tunnel floor and 8"+ ceiling, and 48" riser.

You could make a 6" J-tube with the same figures; it would look more stretched out, but would still hold standard firewood. This matters because you really want your wood to fit completely within the feed so you can cover it quickly in case of any emergency, or just as part of normal operation - I find mine operates best with the feed around 3/4 covered, don't need as much air as flows through an unrestricted opening.

That sounds great, thanks a lot.