Here’s how I cut and stacked my fire brick to create the J-tube and internal flue stack. Horizontal burn section is only 5.5″ long, 3.5″w, 3.25″h. Internal flue will be 3.5″x3.5″ inside, 24″h. Ratio of flue height to burn tube more than 4:1.
Here are the critical numbers…
* Tank is a salvaged 17gal compressor tank with 1/8″ thick walls, 36″ long by 12″ I.D.
* Vertical flue stack is 3 groups of 9″ long fire brick, 3.5″x3.5″x27″ (12.25 sq-in across, about the same as a 4″ round pipe).
* Vertical stack surrounded by 8″ x 24″ galvanized pipe with insulation stuffed in the open spaces.
* Gap at the top of the internal flue is 2″ from the center of the tank (A little less at the edges because of the convex surface).
* Gap between the 8″ pipe and I.D. of the tank is 2″.
* The horizontal burn tunnel is 5.5″ long (measured at the top edges), 3.5″W x 3.25″ H (11.375 sq-in across).
* Vertical feed tube is 3.5″W x 3.25″D x 7.75″H (measured from the top edge to bottom inside).
Many thanks to my Justin.tv regular nerd herd who helped greatly with small tips and suggestions along the way. Tippy4u, Critterwindow, Shubus, Adirondacks4me, Lwblack, Kane48, Outsider007 and many others.
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#323 Rocket Stove J-tube construction wood burning