The paper presents the results of analysis of different renovation strategies for minimization of energy consumption and CO2 emission in museum buildings. This category of buildings is very challenging in the process of renovation towards nZEB, having in mind their value in context of culturally significant buildings. The legislation of EU countries suggests different levels of requirements for nZEB for museums and these levels are not accurately defined in every EU country, thus there is still a lack of experience regarding the strategies and exact boundaries to achieve nZEB. This analysis was done for the museum building in Belgrade, Serbia, built in the period of 1927 to 1929 and protected by the Institute for the Protection of Cultural Monuments of the City of Belgrade as a cultural heritage. Possible primary energy reduction after the implementation of energy efficiency measures was over 80%, while the possible CO2 emission reduction was over 70%. The results showed that the proper renovation, in correlation with the permitted energy efficiency measures for the protected building envelopes, could provide nZEB level even for the museum buildings, according to some of the EU countries criteria. Thus, the paper offers insights into the critical discussion regarding the future limits that should be set to provide optimal solutions for energy renovation strategies for heritage buildings with a possibility of achieving nZEB.