This is just a mortar-free dry-stack mockup of an 8 inch system. It uses fifty-nine firebrick splits for the heat riser, feed tube, and the sides and ceiling of the burn tunnel. It also uses eight 7″ square concrete pavers for the floor. The interior dimensions of the burn tunnel are 5 3/4″ tall by 8 1/8″ inch wide, and the heat riser is 7″ square. Two of the firebricks need to be trimmed a bit for everything to fit more smoothly, so this iteration was slightly off at the feed tube and the bottom of the heat riser.
Once lit, it drew nicely, roared/purred a little, and produced very little smoke, just a bit at the beginning and at the end of the burn. Note that the vertical heat riser is around twice as long as the horizontal burn tunnel. Relatively taller heat riser corresponds to a greater convective draw. It could be taller still to be at a reasonable height for cooking on, which should also improve draw. The next component to test will be the additional insulation around the heat riser, which should improve draw and efficiency of combustion.