Once the firebox is complete the lintel is set. Ceramic wool allows for the core to expand while functioning as a gas tight gasket. After the firebox, the throat is built corbelling back and bringing the gases from the fire-box behind the oven.
Once behind the oven the hot gasses travel up spilling over top of the oven into the two (side) down channels.
A top view of where the heat travels from the center channels into the side channels and then down the side of the heater. The circle in the back is the up channel which connects to the chimney.
This heater contains what is called a white oven as no fire or gasses actually go inside of it. A white oven is heated by the hot gasses that surround it. In this heater, the oven is heated below by the fire-box, then the gas travel behind it heating the back, they spill over the top and then travel downwards along side of the oven thus heating the oven on four sides.
Next the capstones are placed, the chimney connections are made and the heater is complete.