Increased energy efficiency of the building stock is one of the main tools to reduce climate change. Improved airtightness of the building envelope has a side effect – the need for higher ventilation rates which, in turn, lead to a higher energy bill and reduced indoor air quality. This creates an energy efficiency – indoor air quality dilemma. This study evaluates the dilemma impact on the gross domestic product (GDP). System dynamics modelling is applied to answer this question. The education system and labour market of Latvia is used as the case study. Simulation results show that even if all education buildings in Latvia have improved energy efficiency performance and have a significant reduction of outdoor CO2 level, indoor CO2 is very high if no mechanical ventilation is used. The best solution is to increase energy efficiency while providing good indoor air quality by operating mechanical ventilation since the increase in GDP provides financial sources for further energy efficiency measures.