The approach of finite element method (FEM) for simulation of thermal state of space apparatus and heat pipes integrated is presented. The practical tool discussed is 2D finite software package “HEAT'90”. Questions dealing with modeling of 2D construction, accuracy of simplification of 3D objects to pseudo 3D are under consideration. Several practically used cases of heat pipes connections with surrounding are analyzed: heat pipes are installed onto surface of device, heat pipes are inset into honeycomb panels, heat pipe crossing. Samples of simulation of heat pipe network for honeycomb panels illustrate the range of possibilities to forecast the thermal state of complicated ramified systems by using non traditional numerical FEM analyzer.