Heat transfer through window surfaces is one of the most important contributions to energy losses in buildings. Therefore, great efforts are made to design new window frames and glass assemblies with low thermalconductance. At the same time, it is also necessary to develop accurate measurement techniques in thermal characterisation of the above-mentioned building components. In this paper the authors show an innovativemeasurementmethod mainly based on radiative heat transfer (instead of the traditional convective one) which allows window thermalconductancemeasurements with corresponding uncertainty budget evaluation. The authors used the 3D finite volume software FLUENT® to design the experimental apparatus. The numerical results have been employed for the system optimisation and metrological characterisation.