Energy-efficient windows are being used to increase the thermal insulation of a fa & ccedil;ade. Such insulating windows contain an ultra-thin, multilayered, transparent silver coating that acts as an infrared mirror which significantly reduces thermal losses that occur through radiation from inside the building. These so-called lowemissivity coatings revolutionized the field of building insulation but also decreased solar heat gain coefficient which reduces the potential for energy savings during winter. Insulating windows in cold climates should achieve a selective behavior in the transmittance of EM waves. Ideally, solar energy should be transmitted and mid-infrared radiation reflected, thus reducing the heating needs in buildings. This scientific paper presents a numerical investigation based on finite-difference time-domain (FDTD) focused on the optical transmission characteristics of silver plasmonic square nanohole arrays and explores their potential application in insulating windows. It is found that a nanohole array with a periodicity of 350 nm and a linewidth of 50 nm gives outstanding properties and represents a good candidate to achieve high solar heat gain in low-e coatings. The findings contribute to the understanding of plasmonic effects in nanohole arrays and offer insights into the practical application of such structures in the development of advanced insulating windows with enhanced optical performance.