A firebox assembly for generating smoke and conveying controlled amounts of smoke and air for a kamado oven. A firebox assembly has a door leading to a fire chamber, in turn, having an exit opening for smoke to flow into a smoke chamber. A chimney connected to the smoke chamber has slide gates to control the flow of smoke from the smoke chamber into the kamado oven. Further, the gates allow the smoke to be exhausted to the atmosphere and further allow atmospheric air to enter into the chimney eventually flowing to the kamado oven.