RMH sketchup drawing for 150mm diameter J tube

Attached: drawing of 150mm RMH based on kiln bricks 225x110x75.

Happy to give link to an upload the of sketchup file this was done with if anyone wants it. Please just drop a message below.

https://filebin.net/x01xndcufdev2cnp Sketchup file is here.

This is my third RMH build with 6" J tube.

There are two types of oil drums in UK with slightly different height width sizes. I've used both. found that it's best to wrap the whole of the back end of the J tube and the riser with ceramic blanket (tied with wire) and then measure diameter before cutting out the top (which will become the bottom) of the barrel. Have the end of your ducting already in place so you can mark and cut for this at the same time.
Stuff more ceramic blanket in the gaps before wasting fireclay.

These are my first posts to permies, but I'd love to say a huge "Thank you!" to everyone who contributes as I've been a reader for years. I've built my own 6mx7m cabin (straw bale, timber frame) , 4mx7m workshop, and even a woodfired tub. All thanks to info from this site! Big hugs!

JJ

Welcome to permies Jjuk.

Hi Jjuk;
I was just looking at your numbers on the six-inch J-Tube
I see an issue, you have the covered portion of the burn tunnel at 450mm (18") (This should be 10-12" (250mm-300mm)
The total length of the burn tunnel is 750mm (29.5"). (This one should be no more than 24" ( 600mm)

I tried this myself many years ago.
Here is what happened.
My J-Tube roared; I was very happy.
For about 3 months... and then in the middle of a Montana winter, she started acting sick.
Just not burning as it had been. I was beside myself, it is the middle of winter in northern Montana...
I had no choice but to pick a day that was marginally warmer and open her up in the middle of winter!
What I found required a partial rebuild (OH SHIT) !!!

This is when I discovered just how wonderful working with clay mortar is!
Bricks just pop apart with a rubber mallet; the mortar goes in a bucket to be rehydrated and reused.

What had happened was (unknown to me) an incomplete burn, but you sure could not tell that for the first 2 months of operation!
Ash buildup had plugged my transition area and almost all of my piped mass!
That all needed to be vacuumed or blown out; and the burn tunnel roof had to be shortened to 10" (250mm).
Once I did that (and it only took four hours!), my J-Tube Dragon was back roaring around our mountain valley, and she stayed that way for the next six years, until I replaced her with my first Batchbox!