Groundwater advection is commonly neglected in the design of ground-coupled, vertical borehole heat exchangers. In this work, the efficiency of heat transfer from a vertical borehole with groundwater advection is investigated by numerical simulations. The actual borehole geometry is accounted for, resulting in a perturbed flow field. The present results are compared with the analytical solution for the transient, two-dimensional heat convection around a line heat source derived by Diao et al. (2004). A wide range of viable Peclet numbers is considered.