Computational fluid dynamics discrete element method simulations of a 3D fluidized bed at nonisothermal conditions are presented. Hot gas injection into a colder bed that is slightly above minimum fluidization conditions is modeled in a 3D square bed containing up to 8 million particles. In this study, bubbles formed in monodisperse beds of different glass particle sizes (0.25, 0.5, 0.75, and 1 mm) and using hot-gas-injection temperatures ranging from 700 to 1100 K are analyzed. Bubble heat-transfer coefficients in 3D fluidized beds are reported and compared with theoretical predictions on the basis of the Davidson and Harrison model.