This library contains CATHeaPS-FatCat (CATHeaPS v3), which represents the mature evolution of the CATHeaPS-Kitten (v1&2) framework, adding robust modules for integrating openly accessible Energy Performance Certificate (EPC) data to provide stakeholders with preliminary insights into the direct impacts of property retrofitting. CATHeaPS is an open-access modelling tool designed to assess the techno-environmental-economic impacts of decarbonising thermal systems. Developed through a collaboration between the CeNZ-HighDB and GALLANT, the tool empowers local councils, community energy groups, and stakeholders to evaluate heat network feasibility and retrofit strategies using publicly available data.