Renovating the residential stock for lower energy consumption is significant in achieving carbon neutrality in Europe. The study examines several renovation scenarios’ impact on building energy consumption and CO2 emissions through building level simulations. The demo building was a Finnish apartment building built in 1950s, representing old heritage and protected building stock without access to the external wall, window or ventilation system renovations. The analysed renovation scenarios consist of different renovation measures, including balancing radiator network, adding roof thermal insulation, installing ground source heat pump (GSHP), low temperature water radiator system, and electric boiler. In addition, these renovation scenarios’ economic feasibility is revealed by discounted payback periods. The results show that the renovation scenario comprising GSHP, electric boiler, and low temperature water radiator system had the most significant impact, reducing building CO2 emissions by around 79%. In comparison, the impact of the roof thermal insulation was minor. However, balancing radiator network slightly increased CO2 emissions by 1%, while it led to better indoor thermal comfort. As for their economic feasibility, the roof thermal insulation conserved the shortest discounted payback period, 2.8 years, mainly due to its low investment cost. The final cost-effective case, including GSHP, electric boiler, and roof thermal insulation, reduced building CO2 emissions by 78%, and it possesses a discounted payback period of 7.1 years.