Since the 20th century, the temperature has risen, worldwide, due to climate change causing global warming. Such phenomena have resulted in thermal dissatisfaction within various buildings indoor spaces including Egyptian Coptic Orthodox churches. Heritage churches designs have always implemented passive strategies to provide indoor thermal comfort. However, modern churches design tend to use active strategies to provide indoor thermal satisfaction instead of referring to the use of passive designs. Accordingly, the main purpose of this research is to identify a set of guidelines to enhance indoor thermal comfort in modern Coptic Orthodox churches using passive design strategies. The research has adapted a mixed method approach where an in-depth literature review resulting a qualitative summary of passive techniques used in heritage Coptic churches, then followed by a comparative analysis between two Egyptian case studies; the first is a heritage church (St. Barbarah church) and the other is modern which is (Virgin Mary church) based on the deducted passive strategies from the literature. Moreover, an applicable simulation for varying the methodology, using Design Builder, where the modern church will be simulated and tested for thermal comfort before and after modifying it using the passive strategies deducted from the literature. The research’s main findings were the list of passive techniques that could be used to enhance the indoor thermal comfort, while the simulation experimental results where related to a typical summer week, showing that for the average air temperature and the average solar gains, the triple glazing was the most effective in causing indoor thermal comfort. But, for the average relative humidity and average of total fresh air, insulation has shown to be most effective in providing enhanced indoor thermal comfort. To conclude, a set of guidelines has been deduced from the methods adapted in the research showing the most suitable and applicable passive design strategies that could be used inside Coptic Orthodox churches to enhance indoor thermal comfort.