Considering the determinant role of glazing systems in energy consumption, it is imperative to survey the thermal performance of double coated glazing systems in accordance with the harsh climatic conditions and available local and foreign products' situation. In this paper, the radiative properties of local coated and non-coated glazing units are measured by the spectrophotometer and emissometer apparatus. These thermal and solar properties were not available in any datasheet. In the second step, through the accurate calculation method of EnergyPlus software, the amount of energy loss due to the radiative properties of glazing units was simulated in two extreme climates (very hot and humid climate and cold climate). By choosing the simulation method instead of real measurements in this step, it became possible to evaluate the effect of different parameters (such as climate, orientation and glazing specification) on the annual energy loss through the glazing units by eliminating other factors like energy transfer through opaque surfaces and ventilation. The simulation results indicate that using double glazing unit with low-E coating on the third surface (from the exterior) of the double glazing, significantly reduces energy consumption of the glass unit (up to 97 percent) for all orientations in the cold climate. In hot climates like Bandarabbas, using reflective coatings (with dark blue color) in double glazing units is the best possible alternative since it lessens the energy transfer through the glass unit (up to 70 percent) compared to the clear double glazed ones.