Building integrated geothermal foundations are earth-to-air heat exchanger (EAHE) that offer alternative to numerous technical problems inherent to the traditional EAHE. However, an accurate understanding of their thermal behavior is crucial to ensure the best energy gain and an economic viability of this system. The study is based on experimental results obtained on a full-scale ventilated foundation. An accurate and global energy analysis relies on a detailed instrumentation and a one-year monitoring campaign. They focus on power, daily energy gains, surface energy gains, coefficient of performance, operation time and temperature dampening indicators. The results show that this system is very efficient for cooling, especially when compared to traditional EAHE. This performance is almost exclusively due to the contribution of the first half of the foundation length. The performance is satisfying in heating mode but could be improved using a simple on/off control of the airflow. An indicator is also proposed to understand the source of the heating / cooling fluxes. (C) 2019 Elsevier B.V. All rights reserved.