The cooling loads of a building are also dependent on the amount of heat gained from the outside, and with the need to improve the energy efficiency of buildings in order to reduce energy waste and carbon footprint and ensure access to energy for more people, the right window types have to be utilized. This work used the standard cooling load estimation method to carry out an analytical study of the effects of the U-value and shading coefficient of window glasses on the cooling load of a building under the climatic conditions of Owerri, Nigeria. The results show that increasing the number of window panes from single to double and triple reduced the amount of heat gain into the cooling space. It was also observed that reflective glasses reduce heat gain into the building as opposed to the uncoated glasses predominantly used in Owerri. Also, the presence of argon gas in the space between the panes of the double and triple-glazed windows helped in further reducing the heat gains as against air, which is predominantly used. The reflective double glazing, with an 84.8% reduction in heat gains, showed the greatest reduction as against the uncoated single glazing when considering heat gain through radiation, but the high-performance green-tinted, argon-filled triple-glazed glass showed the greatest reduction in cooling load generally. The study concluded that choosing the right U-value and shading coefficient for windows will help in improving building energy efficiency by reducing energy demand and, by extension, lead to cost savings, reduction of carbon footprint, and achievement of net-zero energy in the built environment.