Miniature model of a J-tube RMH with mass

Hey fellow Permies,
I was wondering how small I could possibly go if I were to build a miniature model of a J-Tube RMH. Ideally the model would actually work, maybe even have a little mass bench. I want to make it to take it to an artist market where ideally it would attract some people that then talk to me and maybe hire me for stove building in the future.

I read a couple of times that smaller than 4" is not recommended for a real heater. That makes sense to me. Has anyone tried building something like a 2" or maybe even 1" system as a model? It wouldn't have to actually burn too clean or for hours.

Hi Ben;
Neat idea.
The first thought I had while reading your post was, will the Market let you have a wood fire, even as a short demo?
Perhaps, in Spain, they will?
Paul, Mud, and I were at the Missoula fairgrounds in a sea of green grass, but we absolutely were not allowed to light off Mud's cottage rocket with a bell.

Next, I'm wondering what material you would use to create a working 2"-3" J-Tube?
CF Board?  Clay brick?

So, here is an idea.
Instead of a working model, what about a demo model with, say, the side of the burn tunnel exposed and the riser sitting exposed.
You could explain how a stratification chamber works.
You could have photos of working J-Tubes and of a new cottage rocket I recently saw that is almost complete. Feel free to use any of my photos, either of my J-Tube or the Batchboxes.
Smart people will be fascinated by the whole idea!  Some will rush home, look them up, and build their own. Others will look at you in wonder and ask if you built them for people.

Hi Tom,
thanks for your answer.
They're quite paranoid in Spain when it comes to open fire, but then rule following is more relaxed. But a fair point. I don't know.

I was definitely thinking smaller than 3", something that would ideally fit on the table... Like those cool steam engine models.

I would try doing it in cob and cut offs from refractory brick.

But you're probably right. Maybe I'll opt for one that doesn't work that shows a J-tube cut in half, with a can as a barrel.

And thanks for your offer about your photos.

Davin has made a tiny model that may be of interest as a thing to play with - not working, but a 3d representation perhaps:



See his thread :here Mind you, Davin hasn't been on for a little  while....

I have made a few small J tubes, they are table top size.

About ten years ago some friends and I built a functioning demo model of a 6" J-tube with a single half-barrel bell bench. We moved it in components and materials, and set it up for an Earth Day fair in April. It worked beautifully and there was no visible exhaust, only a heat shimmer, and the exhaust was comfortable to breathe, but unfortunately there was a heat wave and it was 90 degrees F while we were running the heater. Nobody wanted to sit on it or could tell how effectively it made warmth.

All that is to say that if you have a couple of people and sufficient time to prepare the parts for quick assembly, a functioning demo is quite possible. A 5" J-tube with a small barrel over the riser and a half-barrel bell bench and 4' stovepipe chimney would most likely function while being portable enough for a small crew to handle.

Fox James wrote:I have made a few small J tubes, they are table top size.

Now that is pretty cool.

Do you shape your burn chambers to foster the coriolis effect?

The coriolis effect only works on a globalish scale, not in something one person can hold. Vortexes and intentional turbulence are certainly possible. The square sharp edges of a J-tube's bends do this effectively. Plenty of people have tried additional tricks to make vortexes... I don't know that they have shown greater combustion effectiveness than the classic design.

Glenn Herbert wrote:About ten years ago some friends and I built a functioning demo model of a 6" J-tube with a single half-barrel bell bench. We moved it in components and materials, and set it up for an Earth Day fair in April.

Ooh, you've all given me ideas! Did you cover the barrel bench with mass? I'm wondering if we could do a demonstration garden somewhere like gardeners' world live - an ecofriendly patio heater as a way in to Rocket heaters going mainstream....maybe a subject for a different thread though...

Hi,

look at this:

Thanks Jan!
That’s what I had in mind.
Ideally even smaller, but then I guess it won’t burn correctly anymore.

The one in this video is not shown fully functioning. I wish they had put wood in properly and demonstrated it working. Building one from cob would work better, as the metal probably keeps it from getting hot enough to burn well.

I would stick to a short system with a bell that would have a better chance of building up draft. Even a 4" system would probably work in that case. I once built a dry-stacked mockup of a 4" batch box core which worked great, with double rams-horn vortex and everything. That with a small bell, perhaps a metal box that would lower over the core, could be easily transported and function well.


Our demo did not have real mass around the half barrel, just some bricks stacked and concrete pavers on top. We had a box frame that could have held a pebble bed, but with the day being so hot we did not feel it was worthwhile trying to do that.