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Many homes may have older, less energy-efficient windows that studies report add-up to 25-30 percent loss of heated or cooled air. About 65 percent of owner-occupied homes were built over 30 years ago, before most state energy codes were created.

Because of their high cost, replacement windows may take decades to earn their keep and supply delays may add weeks or even several months to their installation. Window films offer similar energy savings and the reduction of sun damage but do it more cost-effectively, according to the IWFA.

Advances in window film technology allow many to act as a shield, blocking room heat as it tries to escape through the windows and reflecting it back inside in winter, while also repelling much of the sun’s solar heat in summer.

“Window films that are permanently affixed to windows still in good condition may offer significant energy savings in both winter and summer, and can be professionally installed in a day or less,” said Darrell Smith, executive director of the IWFA.

“While the low winter sun may provide some passive heat, it also causes harsh glare, contributes to costly fading of furnishings and floors and may also harm the skin and eyes from its ultraviolet (UV) rays,” he added.

At about one-seventh the cost of full replacement windows, window films improve the energy savings of existing windows and block 99 percent of the sun’s UV rays that contribute to interior furnishings fade. Many of them have manufacturer warranties of 15-20 years or more.

UV rays are ever present, and up to 80 percent of the sun’s rays can pene¬trate clouds. In winter, when there is snow and/or ice on the ground, the sun’s light is reflected upward, so windows are impacted by glare from two angles, from above and also from the ground up.