Abstract: A heat source device is provided for supplying indirect heat to a cooking grill such as a charcoal grill. The heat source device includes a heat chamber body to contain a heat source remotely spaced from the grill, an access door to access the heat source, and a mounting adapter to couple the heat source device to the grill. The heat source device may be configured to couple to an existing charcoal grill, as in a retrofit arrangement in which the mounting adapter couples to an ash catcher mount of the grill. The heat source device allows a user to feed or maintain a fuel source in the heat chamber to regulate the temperature in the grill without the need to open the grill, remove the food, or remove or open the cooking surface. If the heat source is maintained, the grill may operate indefinitely.