Troubleshooting my mock-up

My mock up is smoking. MY Stack is 8" carbon steel 30". My burn tunnel. 15" x 6" x 5" and my fire box is 8" deep 7"x7 ". Its drafting about 3/4 Maybe more.. I keep raising the heat riser above the 30" right now about 4 brick but it doesn't seem to help. Is it beacuse its not mortared?

Phillip Baldwin : If your mockup consists of dry stacking bricks you May have a problem ! You can create a bucket of clay slurry about like good Pancake batter

And dip your dry brick into water for about 3-5 seconds and then into your clay slurry this will nicely seal up all the air gaps but the bricks should come back apart

by rapping one against the next one !

You have not said what you are using for insulation around your stack Which I am assuming is what you are calling your Heat Riser

You will want a minimum of 2'' between the very top of that stack/heat riser, and a very generous amount of space where the cooling and vertically falling exhaust

gases turn at right angles to flow horizontally into your thermal mass, this area and the barrel should be well sealed with a " T" and cap for a clean out at that location!

As soon as the barrel goes over the top of the Heat Riser a vertical chimney should be raised ! This should prove that you have successfully constructed your Rocket

Burner so that when you have both the Rocket and its thermal mass mated together if you have any problems then you know the problem has to be in the thermal

mass .

Hope this is timely and helps ! Pictures are always a help if you can manage ! For the good of the craft . Big AL

Late note this should help !


https://permies.com/t/43625/introductions/Universal
https://permies.com/t/34193/tnk/permies-works-links-threads A.L.

Yeah so far I've had dry brick. I must have overlooked the clay dipping in Iantos book. As for Insulation and the barrel and chimney, I simply hadn't made it that far. I was under the impression it should work, then I build the rest inside after I rebuild the same model that I tore down. Am I incorect?
Either way I was going to go with vermiculite for insulation wrapped with mesh. Let me know, if I need to Insulate, before I fire up the mockup.

Phillip, some observations and supplementary notes:

Ideally you want a consistent CSA throughout the J-tube rocket burner beginning with the wood feed. I.e. the burn tunnel at 5 x 6 = 30 CSA compared to the 7 x 7 = 49 CSA of the wood feed. That's makes operation somewhat problematic and is typically a recipe for smoke back. As is your wood feed is sized for an 8" system while the burn tunnel dimensions are for a 6" system.

And at the risk that you may already be aware of this, I'll mention it nonetheless. When burn tunnels are not constructed perfectly square, it is recommended to have the larger dimension as height. Tall and narrow burn tunnels are better than short and wide.

Okay, heres the 411 on my 6" burn tunnel . My journey with the rmh starts last year at this time. Watching too much you tube I built an 8" rocket mass heater out 1/4" carbon steel. It roared! I then made a 10" out of carbon steel, it also roared!
Then, the kind folks here at permies informed my of my "steel rmh folly". I figured I should buy Ianto's book. When My first mock up failed, because I hadn't mocked it up without the clay as mentioned it above I rebricked my mockup to match my carbon steel versions, wich had 2" smaller burn tube, than feed tube and stack. I'm not saying I did it correctly, I'm a novice, however it does draft now whereas it didn't at first. I will alter it back to consistent dimensions if the clay mock-mortar will fix my problems. Keep the feed back coming, I need all the information possible.