The firebox is also sometimes called the fire pit and is located on one side of the smoker. The firebox is typically on the side of the smoker so that direct heat isn't below the meat. Fireboxes are used to assist cooks when using the indirect cooking method for their smoker. The firebox is composed of an adjustable air intake, a grate that is placed directly over the fire, an exit for the heat and a lid that includes a grilling surface.
Clean the grate so that it doesn't become burned from being over the fire. The grate especially needs to be clean so that air is able to properly flow under the wood or charcoal.
Place charcoal and wood into the grate. Adjust the air intake and exit before starting the fire. You want to make sure that the smoke will be able to exit the firebox and enter the cooking chamber smoothly. You may need to adjust the air intake more once the fire is going in order to control the speed in which the fire burns and the temperature of heat in the chamber.
Make sure that the firebox door is attached at a low level towards the fire and sufficiently attached to the smoker chamber. You'll want to make sure that the air flows under the burning fire for the best ventilation and to avoid overheating.
Make sure a baffle is installed between the firebox and smoker chamber. The baffle will help to deflect the smoke and heat down to be under the meat. If there is no baffle used then the heat will go over the meat and the indirect cooking method will not work.
Begin grilling by starting the fire. When using a firebox and performing the indirect cooking method you must frequently turn the meat and extend the cooking time to much longer than what you're used to since you'll be cooking around 225 degrees Fahrenheit instead of the normal smoking temperatures of 500 to 700 degrees Fahrenheit.