Building a RMH with ceramic clear glass front window with airwash

Hi all, so I'm going to build a RMH. I have quite a bit of experience building various types of stoves including rocket stoves, gasifiers like the Solo stove with secondary burn etc and even designed my own woodfired barrel oven that uses the same principles as the Solo oven(I However, I was using the design long before Solo stove was even a company..I'll post a Youtube link for my Barrel oven at the end of this for anyone interested in that. I don't sell them, just for informational purposes to share the idea)

So I've been comparing the RMH Jtube design with the Batch Box design. I prefer the simplicity of the Jtube RMH, however I'm not a fan of feeding sticks into fires rocket stove style and I feel like the Jtube portion of the design is not necessary. For my RMH, I will be using a large ceramic clear glass window on the front so I can watch a nice fire in the winter. I'll have the air intake above the glass so it washes down over  the glass to keep it clean. In my experience making stoves, I've found that the #1 important thing to having a clean and efficient burn is insulating the burn chamber to get temps way up. With intake air washing down over the glass and taking all the heat back into the fire through the exhaust, I feel having an insulated front as on the Jtube design isnt really important, since the air is coming in from the front. as long as the top and sides of the burn chamber are insulated, as well as the initial first chimney that goes up into the 55 gal barrel, temps will get exceedingly hot for a clean efficient burn.

I'll be making the burn chamber large so as to fit regular size split firewood/logs and just need to finalize the door design, whether to have the front glass open as the door, or have it just be a permanent window, and make a door on top that is insulated so the wood drops down in vertically from the top like a J tube, but after lighting the fire and closing the top insulated door (100% sealed) the air wash intake (adjustable) on the face above the front glass would be the air source, not the  door on top.

I'm wondering which would have better start up drafting properties? I'm leaning toward making the glass into a front door. Open to any feedback, ideas, or criticism, thanks. Oh and here's my oven video I designed
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Welcome to permies, Nate. Sounds like you have already been studying rocket science

You say you like the simplicity of the J-tube over the batch box, but it sounds like you are introducing as much complexity as a batch box with doors and air washing glass. If you have a chamber large enough to load with a batch of larger logs, the geometry of the burn tunnel and riser goes away and you no longer have the turbulence of the fast right angle bend. To bring that back, you could make a constriction... like a batch box has.

A top loading firebox may be fine for starting; what happens when the first load burns down and you want to refill it while it is still hot? You will have a strong push for hot gases and smoke to go straight up into your face as you are loading. Draft will not overcome that for a large lid. A front door will have less of that issue.

Peter van den Berg spent literally years and many dozens of iterations with professional testing equipment to optimize the batch box design. I believe all of the issues you mention have been addressed in his work.

Hi Nate, if you forward  wind my video to around 2minutes you can see my version of a glass front J tube with airwash !

Fox James wrote:Hi Nate, if you forward  wind my video to around 2minutes you can see my version of a glass front J tube with airwash !

Looks like a great design, and the dual wall glass and top glass door is a nice touch to help retain heat. I'd rather just use a single pane for cost and simplicity if the heat retention is adequate which I think it will be, but dual pane is always a nice option to consider.

Glenn Herbert wrote:Welcome to permies, Nate. Sounds like you have already been studying rocket science

You say you like the simplicity of the J-tube over the batch box, but it sounds like you are introducing as much complexity as a batch box with doors and air washing glass. If you have a chamber large enough to load with a batch of larger logs, the geometry of the burn tunnel and riser goes away and you no longer have the turbulence of the fast right angle bend. To bring that back, you could make a constriction... like a batch box has.

A top loading firebox may be fine for starting; what happens when the first load burns down and you want to refill it while it is still hot? You will have a strong push for hot gases and smoke to go straight up into your face as you are loading. Draft will not overcome that for a large lid. A front door will have less of that issue.

Peter van den Berg spent literally years and many dozens of iterations with professional testing equipment to optimize the batch box design. I believe all of the issues you mention have been addressed in his work.

Thanks for the input, I'll have to look closer at the batch box design. When I said I prefered the Simplicity of the J tube, I was mostly referring to the lack of secondary air intakes, a V shaped bottom (at least from the few pics I saw on a quick google image search). I'm a fabricator and have no problem building a more complex stove if needed, and will look into the batch box design closer, but I prefer to keep things simple and not mess with secondary air ports.

I did watch a couple videos of the Batch box whicj said smoke coming out the front door was sometimes an issue, which makes me think it doesn't draft as well as the Jtube in certain conditions maybe. I still have a lot of research and video watching thread reading to do, and experimenting to do.

As far as the larger burn chamber slowing down the draft, that's just a matter of compromise, fine tuning and maybe having to reduce the horizontal pipe run through the thermal mass I think. From what I've read with an 8" exhaust, you can run about 50ft of horizontal pipe minus 5ft for every 90 deg bend. So I think I could just find the right ratio of burn box size to horizontal pipe length. I'd be fine even having to cut the horizontal run in half to about 25 ft and then having a much longer vertical thermal mass section to absorb additional heat.

I'm thinking I could also eliminate the downward exhaust flow inside the 55 gal barrel where it comes out of the insulated burn chamber port and turns 180 deg downward. I don't need a low heated sitting bench necessarily, so I'd be fine with having the barrel ontop of the insulated tube section to eliminate any downward flow and just build a higher up horizontal thermal mass heat collector. Maybe this would keep draft flows high with a large burn chamber.

Nate, you should study the batchbox design as it is difficult to beat it on shear performance, the design is very well tested and proven.
Also look up Bell chambers as they are largly superseding piped systems.
https://batchrocket.eu/en/

Fox James wrote:Nate, you should study the batchbox design as it is difficult to beat it on shear performance, the design is very well tested and proven.
Also look up Bell chambers as they are largly superseding piped systems.
https://batchrocket.eu/en/

Thanks, I'll check it out!