Quantitative understanding of heat transfer in fractured media is critical in a wide range of applications, including geothermal energy harvesting. Mathematical models of such systems must account for fluid flow and heat transfer in both complex fracture networks and the ambient rock matrix. Incorporation of individual fractures with millimeter-scale apertures into meter-scale computational domains on which continuum models are discretized would be computationally prohibitive even on modern supercomputers. By exploiting the similarities of the underlying mathematical structure of heat and mass transfer processes, we adopt a mesh-free time-domain particle-tracking method to model heat transfer in highly heterogeneous fractured media. The method is used to model heat extraction from geothermal reservoirs whose fracture networks exhibit fractal properties representative of faults and damage zones. We explore a range of fracture-network properties and experimental conditions in order to study the impact of the fracture-network topology and hydraulic regimes on heat transfer. Our results demonstrate anomalous behavior of heat transfer in fractured environments and a significant impact of the network topology on the performances of geothermal reservoirs.