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Help understanding rocket oven j-tube

Posts: 2081
Location: Olympia, WA - Zone 8a/b
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Hello all,

I'm a novice when it comes to rocket ovens but I would like to build the one that is shown in Paul's rocket oven documentary sometime in the future. The dvd is great but I'm having a bit of trouble with the j-tube.

First, am I getting the basic vocabulary correct? Is it called a j-tube? Is it a batch box too? What exactly does that refer to and what is the alternative?

Also, is the base called the burn tunnel and then the part going up called a heat riser?

My understanding is that it can be built to different dimensions. I have seen threads talking about 4", 6" and 8". What exactly is being measured for those? Is it the open part on the inside?

Say you go with a 6" system. How does that affect the dimensions of the rest of the system? Is there a certain minimum height for the heat riser? How about a maximum height?

As far as building the j-tube. I have seen a couple different versions. Some seem portable and some do not. One looked like it used duraboard on the inside and then some sort of bricks on the outside of the duraboard. Do those bricks have to be fire bricks? Or would regular masonry bricks work?

Are there any basic schematics available for free online anywhere? Even hand drawn would help a lot for me to understand exactly how it is all built. Also, if there are any good YouTube videos that show the construction of a j-tube that is similar to the one used in the documentary that would be helpful too.

Really appreciate any help you all can give with this.
Posts: 607
Location: Wellington, New Zealand
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There's a basic glossary here http://donkey32.proboards.com/thread/732/glossary-terms

The inch refers to the diameter of a theoretical circular riser where secondary combustion occurs. If you use a square riser, or octagonal riser, it's the diameter of a cylinder that fits inside.
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