Quantitative forecasting of site-specific geothermal energy extraction requires computationally efficient simulations of heat transfer between geothermal fluids and ambient rock.Such simulations must rely on adequate representations of both heat transfer mechanisms and geological structures in which these mechanisms occur. In particular, heat transfer in fractured rocks is controlled by properties of the underlying fracture network, which can be modeled by various conceptual representations. This variety comes from the heterogeneity of fracture network properties and from challenges posed byin-situ characterization. We propose to use a mesh-free,particle-based numerical method to gain a better understanding of the impact of the fracture network properties on geothermal performance. Weanalyzehow fracture-network topology and matrix-block size distribution control, respectively, the advective and conductive mechanisms of heat transfer in fractures and ambient matrix, as well as the heat flux exchanged between these structures. We exploretwo different conceptual representations of fracture networksover a range of fracture-generation parameters and hydraulic conditions.