Thermal boundary conditions, such as heat flux, play an important role in the overall context of representing machine tools’ thermal behaviour and their interactions with the environment in a way that is close to reality. In this contribution, the machine tool–environment interface is represented based on the finite-element method and the required parameters are assigned. The term “environment” refers in this paper to the surrounding atmosphere and sometimes the foundation. The approach includes the determination of the relevant environmental boundary conditions, such as convection and heat radiation, and the description of how to integrate them systematically into the finite-element model.