This paper presents a modification of the successive flux estimation algorithm of Pasquier and Marcotte (2013) [1] for computation of the so-called g-functions of small to large-scale ground heat exchanger fields. Fast calculation times are obtained by spectral convolution of the incremental flux signal and the borehole transfer function in an iterative scheme. An initial guess that is close to the solution and easily computable is also suggested for fast convergence. Further gains are obtained through the preprocessing of the transfer functions and the sub-sampling of the g-function. The proposed method was compared against the original successive flux estimation method, as well as two other rapid methods in the literature. Results show that the algorithm proposed in this work is by far the fastest and can generate a 40 year g-function of a large ground heat exchanger field composed of 400 randomly positioned boreholes in less than 4 s. The proposed approach is general and can manage fields composed of different number of boreholes and configurations. Crown Copyright (C) 2020 Published by Elsevier Ltd. All rights reserved.