The ground thermal conductivity and borehole thermal resistance are essential parameters for the design of a ground source heat pump system. As it is hardly possible to obtain sufficiently accurate values of these parameters from geological or soil-profile information, thermal response tests have been developed that provide measurements in situ. These tests have become part of the standard toolkit of the shallow geothermal energy systems engineer, but a systematic evaluation of the different sources of uncertainty (error) and their effect on the quality of the result is lacking. This paper explores the different error sources and shows how they contribute to the final overall error in estimated thermal properties. The results show that the theoretical errors are expected to be on the order of 5% for the soil thermal conductivity and 10-15% for the borehole resistance. The largest contributions to the error of the thermal conductivity are the measured temperature difference, fluid heat capacity and slope of the regression coefficient. The borehole resistance error is mainly influenced by the error of thermal conductivity. (C) 2012 Elsevier Ltd. All rights reserved.