Glenn Herbert wrote:Aside from the rectangular shape not being ideal, looking at the photo reminds me that that stacking method is inherently unstable. At the expense of cutting two bricks a bit shorter and using an extra layer's worth of bricks reoriented at the base, you could rearrange the core to be square and much stronger.
Replace the bottom vertical row of the core with two layers set horizontally, giving a smaller height, and run the heat riser bricks in pinwheel fashion, alternating direction with each course. The bottom course of feed and riser would need a brick cut shorter by the thickness of a brick, so the burn tunnel can be safely bridged. Do that, with the joints clayed up, and I bet it will rocket. You would also need another course of bricks laid flat and pinwheel fashion on the top of the feed, to make up the height lost by the flat layers at the base. This would have the side benefit of giving a wide flat top to the feed surface for more stability (once it is supported by cob enclosing the core.)