Dry stack stove boiling water

I recovered some bricks from the neighbor by chopping off the mortar and stacked them into a little stove just to test out. He even had some old fire bricks! I wanted to play around a little just to see how this all works. So far so good. I put about 15 quarts of water into a pot and did about a 30-40 min burn and the water was warm but not hot. I’m curious if taking this apart and rebuilding it with a J tube will produce something that’s much more efficient. Does extending the flame path really help the efficiency that much? I think just for safety reasons doing a J tube would be better. Much less opportunity for embers to fly out.

Hi Chris;
Well, now you have gone ahead and done it!
There is no hope for you now!
You have been bitten by a baby dragon!
You will find yourself dreaming of Rocket stoves, J-tubes, L-tubes, Peter channels, and five-minute risers...
Wondering how they would work? Perhaps with changes... you could be the one to improve performance...
Before long in your dreams, the words BATCHBOX will float by...  you will start to wonder, what's up with them?
Next thing you know you will be ordering the books to learn how to build such a cool thing!

Now, dry stack those bricks into a proper J-tube with consistent dimensions from start to finish.
Use some mud to seal up the air leaks and watch how fast your water boils then!

Congratulations, you have taken your first steps toward becoming an apprentice Rocket Scientist!  

Haha! Thanks Thomas. Indeed, the baby dragon has bitten me. Alright sounds good. I’ll reconfigure it and seal it up. I guess I need to make another trip to the neighbors house to clean more bricks. He got a whole pile of them when the local school burned down. I had a lot of fun doing this

Ok I’ve rebuilt it as a mini J tube with some mud to seal the air gaps in the bricks. It seems to mostly work well except if I load it up with too many sticks and then it reverses direction and I’m not sure why.
I can upload a short video to YouTube if that helps

A  much better build Chris!
I suspect that your stove was not warmed up enough.
The riser needs to be the hottest portion to maintain a solid draft.
The flames will always take the easy way out if they can.

EDIT) after looking at your photos I would make your riser a couple of bricks taller.

Second what Thomas said. It's all about the ratios, and the 1:2:4 formula is proven to work. This means that the internal length of the riser should be double that of the burn tunnel, which in turn should be double that of the feed tube. Your build is prone to reversal because the feed tube can start acting as a stack and pull the draft the other direction.

OK I’ll see if I can get this closer to the ideal 1:2:4 ratio. Once I’ve got this running properly I’m curious how putting a pot on top of the exit chimney to boil water for canning won’t mess it up and cause it to start back drafting again.

thomas rubino wrote:A  much better build Chris!
I suspect that your stove was not warmed up enough.
The riser needs to be the hottest portion to maintain a solid draft.
The flames will always take the easy way out if they can.

EDIT) after looking at your photos I would make your riser a couple of bricks taller.

Yeah… I started with a little fire and then got excited and put a ton of sticks in lol. I reread the startup section in Weisners Rocket mass heater book and it says to go slowly and make sure the chimney is hot because the J tube is like a kitchen sink bend and wants to plug up with cold air.