Abstract Global sensitivity analysis of the efficiency of borehole thermal energy storage (BTES) during long-term operation on the borehole heat exchanger (BHE) arrangement was investigated to advance understanding of the system’s thermal performance. Three parameters were assessed to determine the BHE arrangement: the first parameter designate the distance between BHE axis in x direction, the second in y direction and the third an angle between top surface of the rock mass and boreholes axis. Conducting research on the real system is extremely expensive, so it was decided to conduct simulation studies utilising a finite element method. The ANSYS software with a newly implemented heat and mass transport model in BHE was used. Based on conducted numerical simulations, and according to the design of the experiment, a multidimensional response surface was achieved. The global sensitivity was conducted based on a response surface model. It was found that the BHE inclination ( S Eeff P 3 = 0.97 – FAST algorithm) has a crucial impact for the BTES efficiency. The area on response surface, where the optimal BHE arrangement to maximise BTES efficiency could be reached, is an inclination P 3 = 0 ° and BHE spacing in the range of P 1 = P 2 = ( 1.5 – 3 m ) .