The polyester film bisects a layer of argon or krypton gas that fills the gap between two glass panes, creating an extra air space that significantly improves the window’s R-value and associated heating and cooling costs. Inspectors and homeowners may become confused regarding the properties of Heat Mirror™ and other green products commonly applied to windows, such as low-E coatings, which also use a reflective layer to reflect infrared energy. Low-E film, however, is made from metal or metal oxide instead of polyester and is physically applied to the glass surface. Unlike Heat Mirror™, a low-E coating does not increase the number of air spaces in an IGU. Debate has persisted for many years concerning which is the better design, with proponents on each side pointing out defects and inefficiencies of the other product. The two designs are sometimes incorporated in the same IGU for additional protection against heat or infrared energy loss.
Amory Lovins is a Colorado resident who pays $0 in energy bills for what may be one of the greenest houses on the planet, according to MSN Money. Heat Mirror™ and other energy-saving features (many of which are covered in InterNACHI’s robust InterNACHI article database) have allowed Lovins to harvest 28 banana crops in his indoor banana jungle without the aid of central heating, despite the fact that his Rocky Mountain estate experiences sub-zero blizzards every winter. There are also plans to install Heat Mirror™ in the Empire State Building’s 6,500 windows as part of the building’s energy retrofit project. According to BusinessWire, the installation of Heat Mirror™ in the windows of New York’s tallest building will decrease energy costs by $400,000, cut solar heat gain in half, and improve the windows’ R-values from R-2 to R-8. Skyscrapers and alpine banana jungles aside, most Heat Mirror™ window film is found in ordinary residential and commercial structures, although it is among the more expensive options available.
InterNACHI inspectors may be on the lookout for older types of Heat Mirror™ that are prone to discoloration, warping, becoming brittle, and seal failure. One such defect is yellowing, caused by impurities that make their way onto the film before it is sealed within the glass panes. Wrinkling is also a problem in older Heat Mirror™, as you can see in the accompanying photo. These problems have largely been resolved in recent years, as Southwall has corrected manufacturing errors and more closely scrutinized their licensed distributors.