There is currently a lack of established calculation method for the geotechnical design of heat exchanger piles. Thermo-mechanical effects are ignored and large overall security factors are therefore applied. This paper presents a new geotechnical numerical design method for heat exchanger piles, based on the load transfer approach. The method is validated on the basis of two in situ measurements. It is shown how the pile design could be adapted and optimized with respect to concrete resistance and the mobilization of the pile shaft friction during the operation of the heat exchange system.