Ground thermal response functions, also well-known as g-functions, have been extensively used for sizing ground heat exchangers and performance analyses of ground coupled heat pump (GCHP) systems. A general approach used to generate g-functions is to define a wall boundary, e.g., uniform temperatures or uniform heat transfer rates. In this work, a TRNSYS g-function generator is proposed that uses the uniform heat transfer rates as a boundary to the finite line source (FLS) model. This boundary can be easily applied to the FLS model and the generating process is computationally rapid. The duct storage (DST) modelTRNSYS type 557are used to test the proposed FLS-based g-function model. Results showed that the DST model was in good agreement with the proposed models but deviated with respect to the other boundary-based models. However, discussions on which the boundary is realistic are not yet completely concluded with this work since the DST model itself uses several simplifications. (C) 2018 Elsevier B.V. All rights reserved.