Using the known physical characteristics of a prototype photovoltaic-thermal (PVT) collector components and raw test data from a prematurely terminated ISO 9806 test, the objective of this study is to reverse engineer a thermal resistance value for the heat exchanger assembly for use in the theoretical TRNSYS model Type 560. Modeling is done using both TRNSYS as well as commercial heat transfer software TAITherm. Performance is measured by the mean absolute error and correlation of the outlet temperature and thermal power, as well as the differences in total thermal energy generated. The results show a thermal resistance of 0.005 to 0.010 m2 K W-1 in TAITherm and 0.010 to 0.040 m2 K W-1 in Type 560. TAITherm gives better statistical indicators which is likely due to the inclusion of thermal mass in the model. The results have informed prototype development and can be used in further systems modeling. © 2017. The Authors.