The article presents the features of mathematical modeling of the heat release during the hardening of composite cellular materials using the example of non-autoclaved foam concrete. The reactions of hardening and structure formation in foam concrete are exothermic and are called hydration reactions. The article lists the technological factors affecting the heat release during hydration. The basis for research and modeling of thermal processes in the structure formation of cellular composite materials is the nonlinear differential equation of non-stationary thermal conductivity with a source distributed over coordinate space and time. In the first stages of modeling, it is advisable to set the boundary conditions and solve a plane problem for one of the coordinates. The mathematical description of the kinetics of heat release of the hydration reaction is presented for an elementary foam concrete sample with a face size of L centimeters. Heat transfer in all directions in the sample is similar due to the ordered cellular structure. As a result, the equations describing the heat release during the hydration of foam concrete along any one axis are obtained. This allows us to determine the course of the heat release process and the temperature distribution at any point in the volume of the composite material.