Which of the following enhances the energy efficiency of windows?

Incorporating low emissivity (low-e) coatings on windows significantly enhances their energy efficiency. Low-e coatings are thin layers of metallic oxides applied to the glass surface, which effectively reflect infrared light while allowing visible light to pass through. This means that during the winter, low-e coatings help keep the heat generated inside a building from escaping, while in the summer, they can reflect external heat, thus keeping the interior cooler. This dual functionality results in improved insulation, reducing reliance on heating and cooling systems, and ultimately leading to lower energy costs.

The other options do not contribute to energy efficiency in the same way. Larger window frames typically result in a larger area of heat transfer due to increased materials, which may decrease energy efficiency. Single-pane windows provide minimal insulation compared to double or triple glazing options, allowing more heat transfer. Unsealed glass can lead to air leakage, which undermines energy efficiency by allowing outside air to affect indoor temperatures.