HI, Don! I’ll try:
Imagine your WK with secondary preheated air added from slots in the restriction. Gases will instantly burst into flames and due to the cylindrical ceramic combustion chamber they swirl both ways, creating an upside down atomic bomb mushroom. Lot’s of turbulence and a clean burn.
The hopper is all inside water mantel and will ofcourse be very tary but heat radiation from hot charcoles, when fuel level gets low, bakes the tar into a hard shiny crust that protects walls from rusting. Hopper holds 150 L 1/2 m logs. It lasts 2-4 hours depending on wood quality.
After combustion the super hot exhaust enters ash deposit/dropbox and than up into 10 heatex tubes. Tubes are easily cleaned occationally from the top hatch. Always only fine white dust.
The boiler manages with only chimney effect, but I’ve added a fan on top of the chimney for easy startup and warm weather. It operates on thermostat (exhaust temp).