Since it's a recurrent problem for newbs, to have a good flue transition.

I ask you to post pics of good ones you have seen, or used yourself.

Please, refrain on the words, just a quick description of the tricks used is sufficient.  So the thread is not getting drowned with babble and arguments.

Thanks a lot everybody.

My small bell plenum (transition area).

This is generally a gorgeous build out. What was wrong with the core? Does this heat an inner courtyard, and partially supply the home as well? --Transitional spaces particularly intrigue me because they inspire neighbors and help beat greedy landlords, realtors and utility companies out of a lot of bucks!

Tom; Read my post on spontaneous combustion, it explains the core rebuilds.  No this heats just our studio/greenhouse.

Good idea to make this thread!

Brief explanation: a rocket combustion unit on wheels and not much room at the back side of the barrel.
Idea: Intersecting the barrel with the flue pipe. Pipe runs tangential and opens where it cuts the barrel.
Advantages: bigger open space and less direction change of the exhaust gases compared to a 90 degree outlet. One of the side openings is the flue connection and the second is capped as clean-out.
Challenge: get the intersection cut to fit. Solved with an Excel template calculation sheet.
Pictures:

Printout of the actual intersection, according to theory:


Checking my math with cardboard tubes, you should get the idea by now:


Template cut out and layed on target area at the actual lower barrel part, 2" above floor for ash deposit space:


Tubes cut (jigsaw), matched, secured with screws and sealed with high-temp automotive silicone (lack of welding equipment):


Opening viewed through the exhaust/cleanout pipe:


Metal "manifold" with cutout for core:


Transition space viewed from the inside:


"Manifold" in place:


Being built in with cob mortar and perlite/clay insulation:


The finished heater is running its exhaust through bell bench in the 4th week now with no hassles.

Hi Ralf ;  All I can say is wow ! Nice work.

Nice one Ralf.

You're not the first one to use this arrangement. But i've only seen one before i think.

How much gap projection and edge length do you have, on top and sides of the transition?

Have you published your build elsewhere? It would be good to have a link to it.

Thanks for posting.

Thanks Thomas & Satamax !

There´s a guy with the nick Manuel over at Donkey's who had the same idea independently and uses it in his builds, but he cuts the pipes by eyeball, which is ok when he cobs them in.
Cutout template rolled around the barrel is 44 cm / 17.5 "  wide and 15 cm/  6" (system size) high, circumference/edge length approx 1 meter / 3.3 feet.
More important to me was the intersection depth that is 11 cm / 4 1/3 " (depth 0 means tubes touch but do not intersect).

The nicest thing about this I discovered: when you open the cleanout you can see straight through to the bench entrance an clean super easy if necessary.
And since the combustion unit is mobile you can hook up the thermal battery left or right depending on where you install it.

The build sequence isn´t published yet, I plan to do so here and at Donkey's, but it will take some time. I want to run the stove for some time and get used to fire it under all atmospheric conditions before I declare success.
Here´s a pic of the finished unit. Flue pipe ends sticking out behind the barrel to the left and right not visible here:

Flue transition in hardware cloth (1/4" wire mesh) clad with clay sand mix.
6" X 19" rectangle cut out of bottom of barrel,  tin snipped curved surface to further 1" and splayed the tabs out, and bent out the two side strips. This gave me something solid to offer the mesh up to. The mesh was left as a single piece where it joined the barrel and bent over and shoved into the clay each side I then snipped along the length towards the barrel (twice). This let me curve it downwards towards the flue overlapping where needed. Extra mesh added to make the final connection to flue

Thanks for the thanks Antoine. It's a pleasure to help! I found the transition the hardest part of the build, so I'm sure others will find your post really useful.

Beginning to cover mesh of manifold with clay where it butts up to barrel.  The cover cap at the bottom is on a short length of flue that leads to manifold, for clean out access. As the manifold took shape, I added more wire mesh overlapping it to get me to the flue pipe. I tried to add clay layer to inside the manifold but bits of that fell in. Smoothed a bit more in, but gave up and added more clay on the topside. Seems to be holding fine.

2015 ready to fire

2016 cosmetic changes made and three coats of lime wash. Bench still not finished, but needed the heat! One of the pluses of using natural materials is that you can mend/change things easily. One house brick used in the feed tube (spanning the opening to the oven)had cracked so replaced with a firebrick, and added some decoration, last summer,

Thanks a lot Lesley.

Here is the transition of my 6 inch rocket.

Then I raised the outer barrel up a bit, and you can see the black area where the hot gasses flow . . .

And final result . . .

Here is my stove after about 3 months of burning every day. As you can see, there is a lot of ash accumulation out of reach from the cleanout port which is why I normally lift my barrel and clean it about twice a season. I may move the cleanout port to help solve this problem however, it also gives me a peek 'under the hood' to inspect the riser (clean the top of the riser) and repair any cracks or other weakening points if needed. Of course ash accumulation varies with what type of wood your burning, if you burn any paper products and of course operator/stove personalities....The only place I can think of that a small amount of ash accumulation is beneficial in this area would be to help form a seal where the bottom of the barrel rests on the cob/brick support.

It seems logical that the more smooth you make all of the 'innards' of your stove the less surface area for the ash to catch on and accumulate. On mine, I surrounded my heat riser with sheet metal which stands up quite well and easy to clean.

A few more pics of the manifold area

Thanksalot Gerry!

I love the offset barrel and big plenum.

This thread needs more pics!

Up! Anybody to share new pics?

This a 8" j tube about seven years old and it works like a dream but it's not at all pretty so I cover it with crochet pads made from old tee shirts. It's in constant use when it's cold and I've cleaned it out a few times and repaired the cob around the burn chamber twice. I'll finish it one day.

I built it, Fabrice reluctantly built the chimney core and cut and helped with lifting on the old heavy water heater I used to surround the chimney and insulation (Perlite). He didn't believe it would work.  
I used an old chimney pot to connect to the barrel which was easy to cut to size and I also cut out an inspection hatch in it. I used the top of the chimney (Which I cut off) to go into the the cob near the barrel and it's used to dry things, warm wine and so on.

Water heater on, burn chamber cobbed in




Experiments with exterior air to burn chamber. I decided that this didn't make much difference the rocketiness and adding another metre to the height of the chimney solved the problem of a good draw.




Second firing, it worked well (inspection hatch covered temporarily until I had cobbed the bench)




Inspection of the joints and cob around the bottom of the barrel after a few burns




Inspection hatch covered with a plate from an old stove




Plan of the workshop. The rayburn heats the water, I preferred to use the rocket for heat only as the pipe run was so long




Just before the pipes exit to the chimney, a boot stash in a dark corner near our back door with a 1 watt LED light which comes on automatically when you come in to take your boots off.




A good clean and repairs to the burn chamber after 5 years




Four dogs, a man, two cats and me and the rest of the dogs are further along the bench...

Pics of my batch manifold and transition. Hope it helps someone.