Historic buildings still perform their role today by being utilized either for their original purpose or a new purpose for which they are adapted. These buildings have specific requirements that inhabitants must follow. These requirements and relating uses and maintenance procedures result from adaptive reuse decisions, which may not be the most optimal scenario. The imperative is that historic buildings are used in a manner that, on the one hand, does not endanger their value related to heritage and tradition, and on the other hand, guarantees a degree of utility for their inhabitants, such as acceptable performance with regards to either air cooling or heating. The challenge is how to optimize the use of energy for either air cooling or heating, provided that adaptive reuse decisions are grounded in certain very specific and very rigid principles. The latter render is extremely difficult to meet the twin challenges of ensuring energy efficiency and thermal comfort for inhabitants while at the same time complying with the adaptive reuse principles. To address this challenge and gain an insight into ways of navigating it, a Post Occupancy Evaluation (POE) is conducted in Former Soldier’s Residence in the Cairo Citadel, Cairo, Egypt, which is now used as the National Organization for Urban Harmony’s (NOUH) administrative head office, this research can be considered as a single domain from which many other possible multi-domains can be investigated while studying the case of adaptive reuse. Other aspects such as indoor environmental quality, air quality, acoustics and lighting might act as multiple approaches appear to be widely used according to this review study, and in the future, the authors intend to test this research with the current single approach used in this research, which is the thermal comfort. POE includes both objective and subjective assessment, the POE limitation at this research to those assessment while a multi-perceptional and behavioral factors might be used as physical, contextual, personal, and others. The simulation and the survey methods were employed consecutively to assess the case study. By considering the research results, it was determined that the building consumes unnecessary energy by its current use of air conditioning system.