The estimation of the vertical displacement of energy pile groups subjected to thermal (and mechanical) loads is needed for a complete geotechnical and structural design of the piles in situations where these foundations may be located sufficiently close to each other. In such situations, interaction and group effects arise among the piles as a consequence of the applied thermal loads, and involve (likewise mechanical loads do) a different behaviour of the piles compared to situations in which they may be located sufficiently far from each other and considered to be single isolated foundations. This paper presents a method that can be used to estimate the thermally induced vertical displacement of any configuration and number of energy piles and to assess the serviceability mechanical performance of such foundations. The method is based on design charts and analytical calculations, and extends to energy piles subjected to thermal (and mechanical) loads the interaction factor method originally proposed for conventional piles subjected to (only) mechanical loads. The objective of this study is to allow the analysis and design of energy pile groups subjected to thermal and mechanical loads to be exhaustively performed.