Cooling a smoker grill allows you to adjust the temperature for slow-cooking food by indirect heat over charcoal. Tender, flavorful barbecue depends on even heat for prolonged smoking, perhaps 12 hours or more for thick cuts such as pork shoulder and beef brisket. Because it is necessary to add more charcoal after a few hours of smoking, the temperature tends to spike right after a fresh load of coal goes on the fire. Cooling the smoker allows you to maintain a steady temperature for uniform cooking.
Adjust the side vents at the bottom of the smoker to regulate temperature. To cool down the smoker, gradually close the bottom vents to cut off the air supply underneath the fire. Close the vents 1/2 inch every few minutes to lower the temperature gradually.
Adjust the top vent or chimney to cool the temperature even lower. The top vent or chimney creates a draft to draw air and smoke up through the grill. Closing these outlets after shutting off the bottom valves will eventually extinguish your coals by suffocating the fire, so use care when adjusting top vents and only close long enough to get the temperature back where you want it.
Raise or remove the lid on the smoker, depending on whether it hinges or detaches, so the heat can dissipate rapidly for fast cooling. This is a technqiue of last resort if you're dealing with a flareup from burning grease or fat and need to extinguish the flames as well as lower the smoker temperature. The main problem with removing the lid to cool off the smoker is that it adds about 20 minutes to half an hour of cooking time whenever the cover is removed, so take it off only when absolutely necessary..
Use the cast-iron grill handle to remove the grills on the smoker and hot pads to lift out the firebox by the wire handles to remove the heat source from the smoker and cool it off rapidly for packing and transportation.
Dump hot charcoal onto sand or bare earth to extinguish the fire away from trees, shrubs and all flammable materials. Lacking a heat source, cast-iron smokers will cool off and be ready for packing in half an hour or less.