Flow-state is a condition where individuals are fully immersed in their mental abilities, wholeheartedly engaged in activities aimed at achieving peak performance. This study explores the relationships between teachers' flow-state within three main learning environments: traditional classrooms, innovative open settings, and forest education. By employing Set and Setting theory which states that our environment directly affects our experience, we investigated teachers' perception of the 'design conditions' through indoor environmental quality (IEQ) such as air quality and lighting and design features, such as furniture arrangement. Data on 119 teachers were collected using closed-ended questionnaires. Our findings indicate the impact of the design conditions on teachers' flow-state. Differences in flow-state levels were observed whereby nature-centric classrooms were found to foster higher flow-state attainment than traditional classrooms. Moreover, age moderates the relationship between design conditions and the cognitive control dimension of teachers' flow-state. Older teachers, in particular, exhibited vulnerability to inferior design conditions, leading to diminished flow-state attainment. These findings underscore the importance of tailored educational environments to optimize the pedagogical experience. They highlight the dynamic interplay between teachers, their flow-states, and the design conditions of learning spaces. This suggests that enhancing these conditions could support better teaching outcomes and teacher well-being.