During heating, the door(s) would be bricked or blocked (kaowool backed plates?). There's a chimney right above the entrance to the firebox- the exhaust gases go through corresponding slots (that's your "exit flue") on the opposite side of the chamber from where they entered and go up the chimney- there's no gas exchange through the doors. Throw in a pizza, dough, a roast, whatever- replace the door plate. Heat can be added without opening the door at all. Maybe I'll add a port to spritz in some water. Plus- if I really want to, I could probably get it to 2300F for disposal of my enemies. In that kiln pic above- the door would be bricked up when it was being fired.