Method of mathematical simulation of heat transfer processes in polymer composite (PC) products with intricate configuration, being an alternative of using up-to-date commercial software complexes has been developed. On the example of PC container with instrumentation and fiberglass electric heaters located in it, a mathematical model describing unsteady temperature field (a system of nonlinear differential heat balance equations for each element) has been formulated. Features of heat transfer between elements (heaters, instrumentation, enclosing structures) were taken into account. The verification of the method was conducted by comparing of theoretical temperature distributions with results of measurements in experiments with simplified variant of the structure. The developed method is effective, in particular, for such PC products as containers, modules, bunkers and vessels. It allows us to specify optimum operation modes for heating elements, operational parameters for conditioners and funs, heat insulation characteristics for providing a given level of air temperature inside objects in winter and summer service periods.