Energy efficient windows are manufactured so that heat is kept inside the home in winter and outside the home in summer. This reduces heating and cooling costs, minimizes energy consumption impacting the environment, and limits the size of the HVAC equipment required for keeping the home comfortable. In climates that mainly require cooling, windows have represented a major source of unwanted heat gain. In recent years, windows have undergone a technological revolution. It is now possible to significantly reduce solar heat gain and improve comfort while providing clear views and daylight. In warm regions, this means that high-performance windows can face into the sun if desired without great energy penalties – although shading techniques remain important.