This study used numerical simulation to investigate the growth conditions of yttrium aluminum garnet (YAG) single crystals by the vertical Bridgman method, and discusses the process performed with or without the installation of a submerged heater (SH). The maximum flow velocity of the melted material surrounding the melt/crystal interface can be decreased, and the deflection of the melt/crystal interface can be changed under various furnace temperature gradients and distances. The minimum of the maximized flow rate indicates that the natural convection can be decreased and controlled. In this manner, the growth rate of crystals increases in an identical environment.