Thinking about a discussion about efficient stoves at the walden effect blog, I designed this rocket stove, with better pre-heating and simplified construction.
Why make firebricks when youu can use two concentric pipes with insulation inbetween? I think this design could be made from off-the-shelf parts. One could use perlite (or vermiculite) as an alternative for rockwool, since that will probably hold the inner pipe in place better. If you forego the extra pre-heating sleeve, the design becomes even simpler.