The relevance of the research is caused by the need to develop new approaches to the study of thermal regimes and thermal losses of underground pipelines and it is confirmed by the main provisions of the Energy Strategy of Russia for the period up to 2030. Underground pipelines are widely used for liquid transportation in various areas, for example, water supply and heat supply, oil pipelines and gas pipelines, technological pipelines of industrial enterprises. When designing an underground piping system, it is necessary to take in-to account nonstationary heat exchange between the ground and the underground pipeline. In many cases this impacts significantly the economics of transportation of energy carriers. The main aim of the research is a numerical analysis of nonstationary thermal conditions and heat losses of underground channel-free pipelines and investigation of temperature fields and patterns of nonstationary heat transfer in the areas of placement of underground non-channel pipelines. Objects of the research are the typical for energy transportation system underground two-pipe ductless pipelines. Pipelines are insulated with polyurethane foam and protective covering waterproofing layer made of polyethylene. Temperature of energy carriers is equal to the average annual temperature of the energy carriers in the supply and return pipelines of the water heating networks during their operation according to the temperature schedule 95/70 °С. The seasonal change in the ambient temperature was calculated according to the law of a simple harmonic oscillation. The investigations were carried out for the climatic conditions of Tomsk. The average heat transfer coefficient at the ground-to-environment interface was 5 W/(m2 * K). Methods: numerical solution of heat transfer problems by the finite element method using the Galerkin approximation, non-uniform fi-nite element mesh, the number of elements of mesh is chosen from the conditions of convergence of the solution; the grid is thickened by the Delaunay method. Results. Scales of heat losses and regularities of nonstationary heat transfer in the zones of underground non-channel pipelines were established. The paper demonstrates the need to take into account the nonstationarity of heat transfer in the zone of underground heat pipes with predictive modeling of their thermal regimes and heat losses. Nonstationary heat transfer in the zone of underground heating networks can have a significant effect, for example, in cases where adjacent communications or engineering facilities are located in the zone of thermal influence of underground pipelines.