Zuhair removed top and bottom of a 200 liter oil drum and cut open and flattened the side. From this sheet metal he shaped the duct, that will be fastened between the top and bottom concrete slabs, outside of the wall. (see picture)
I regretted not to have available an ax or cutlass. Zuhair had to work with good quality tools such as an electrical hand fret saw and a table sheet cutter to cut the sheetmetal parts.
From experience I know that the seemingly more prmitive working with an ax for cutting and a dull cutlass for folding works by far faster and more accurate. Just an underground of dirt works best. I still have to describe these methods in this website.

Hans and myself worked on composing the setup for channels and fire box inside the brick walls.
- Directly over the concrete slabs a metal sheet rest on strips of bricks to facilitate heat exchange between the cold inlet air and the hot gas from the fire box.
- The firebox is wide at the top and narrow at the bottom. This is done by placing two tiles slanted against the outside walls. The space behind the slanted tiles functions as the channel to guide preheated air to the opposite side, where this air can enter between the grates of the fire box.
- As grates of the fire box function four tiles placed between the two slanted outward tiles. The proper distance between the tiles came from placing small stone wedges between the tiles. (see picture)

We expect it to function as follows: Fuel wood slides down from the container to the top of the grates, that is the top edge of the tiles. Burning parts falling off, slide down while burning to a smaller size. Small parts falling through, burn to ashes on a plate positioned under the fire box.
- Hot gas from the fire box moves horizontal through a channel, then up to a channel on top of the first. Then is can escape side ways into the meal ducts as Zuhair has been working on. From there flows out to the chimney (shown near the window).

Hans indicates with the empty container for wood fuel where it will later be positioned (see picture)
Building blocks with a special shape as used this time will later be cast from concrete or heat resistant cement. For this experiment Hans cut them to size with a fast running diamond disk, a very dusty job.