This study evaluates the energy efficiency of the operating modes of a demand-controlled ventilation (DCV) system in a residential building based on CO₂ levels, and determines the impact of CO₂ concentration thresholds, heat recovery and building envelope insulation on the building’s annual energy consumption. This study examines the energy model of Dormitory No. 5 at the Igor Sikorsky Kyiv Polytechnic Institute (Kyiv, Ukraine), created using the DesignBuilder software. It considers a baseline scenario without CO₂ control and DCV scenarios with thresholds of 800, 900, 1000 and 1500 ppm. The analysis showed that the use of DCV reduces the average air change rate from 0.39 to 0.20 / 0.17 / 0.14 / 0.11 1/hour, respectively, resulting in a 54.5% reduction in total annual energy need in scenarios without heat recovery, primarily due to lower heating costs. At the same time, as ventilation rates decrease, the need for cooling increases, reflecting a trade-off between energy efficiency and the building’s summer thermal comfort. It has been shown that the use of exhaust air heat recovery in a mode without CO₂ control allows for a 40.4% reduction in total energy need, whilst combining this with DCV provides a further reduction of 16.7–23.8%. It has also been established that as recovery efficiency increases from 0.5 to 0.8, the annual need for heating decreases by 25.6–40.9%, and for cooling by 2.9–4.6%, with a simultaneous slight reduction in maximum heating and cooling loads. In addition, the impact of insulating the building envelope to the standard level specified in DBN V.2.6-31:2021, as well as options involving a further increase in the level of thermal insulation by 10% and 20%, was analysed. It was found that this reduces the annual heating need by 1.3%, 3.7% and 5.8%, respectively, but is accompanied by an increase in cooling need of 1.5%, 5.5% and 9.2%. A study was also conducted into the possibility of using heat pumps to meet the building’s heating and cooling needs. The study found that the most promising approach for residential buildings is a combination of CO₂-controlled ventilation, heat recovery and modern, highly efficient engineering solutions, which enables a significant reduction in energy consumption whilst maintaining adequate indoor air quality.