Energy Performance Contracting (EPC) can help the European Union (EU) in accelerating the cost-effective renovation of existing building stock. However, there are many risks and barriers that can inhibit the application of EPC. These barriers include uncertainty about building data, lack of quality assurance regarding the post-renovation energy performance, and process complexity. In order to cross these barriers, this paper presents ModSCO. ModSCO is a web application based on a Reduced Order grey-box Model (ROM) able to systematically quantify the energy savings achieved through Energy Conservation Measures (ECMs) utilising the schema of the International Performance Measurement and Verification Protocol (IPMVP). The benefits of utilising ModSCO in terms of accuracy and time savings are demonstrated with a comparison with a whole building energy model developed with IES-VE.