The paper presents a study on existing building stock energy consumption for the country of Latvia and researches the renovation potential of multi-storey apartment buildings and its influence on indoor air quality. The study analyses IAQ parameters and the energy consumption in renovated and non-renovated buildings and presents practical examples of Latvian and Estonian case studies as well. The possible reduction of energy consumption after thermal insulation of apartment buildings and renovation of ventilation systems has been estimated at the state level. Different insulation scenarios and efficiencies of various types of ventilation systems have been evaluated.