We do not suggest going over the amount of 15 briquettes at any given time in the side fire box. Cooking with amounts greater than this will have the potential of getting hot enough to cause damage to the body of the grill such as the finish and warping of the grill. 

(From the owners Manual)

uses but will slow over time. NEVER EXCEED 400 BECAUSE THIS WILL DAMAGE THE FINISH AND CONTRIBUTE TO RUST. PAINT IS NOT WARRANTED AND WILL REQUIRE TOUCH-UP. THIS UNIT IS NOT WARRANTED AGAINST RUST. 2. To START FIRE – stack 15 briquettes in pyramid and saturate with lighter fluid (DON’T USE GASOLINE). Light coals in several places, close lid after briquettes ash over or _ gray, spread them out and start cooking. If one end burns faster, use tongs to move coals from one end to the other for even heat. ALWAYS FOLLOW CHARCOAL AND LIGHTER FLUID MANUFACTURERS’ INSTRUCTIONS AND WARNINGS. USE OUTDOORS ONLY ON NONCOMBUSTIBLE SURFACE – 15’ AWAY FROM WOOD AND COMBUSTIBLE MATERIAL