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  • Writer's pictureJohn@LiteHouse

What's the Deal with Window Films?

Updated: Aug 22, 2023

Home and business owners can use a number of methods to "green" their indoor environment to make the interior more comfortable and reduce heating and cooling costs. One method is to install window film. Window films are represented in three general categories. Most familiar to consumers is a tinted cellophane-type material that can be applied temporarily or used as needed, as in retractable glare-reducing shades. It can also be semi-permanent, such as window tint, which is applied directly to the windows and stays in place.

It can also be permanent, such as the Heat Mirror™ product, which differs from typical films and tints. Their prices range from relatively cheap to very expensive.

Window film or shades can be purchased at the hardware store in rolls with long sheets. It is relatively inexpensive and can be applied directly to windows by a home or business owner to provide shading without blocking all sunlight. This is the same type of tint found on vehicle windows. Heavy window film is sometimes applied to windows to prevent them from shattering into dangerous shards in the event of an impact. Most window films can be cut to fit any size or shape and can be removed using steam or a razor blade and rubbing alcohol.

Heat Mirror™ and low-E coatings are factory installed and permanent. Heat Mirror™ is a clear three-layer polyester film that transmits light through insulated glass units (IGUs) while reflecting long-wave infrared energy. It was developed by Southwall Technologies in 1980 to reduce the amount of solar heat transferred to a home or commercial building, increase occupant comfort and reduce energy costs.

Heat Mirror™ can be installed in an insulated glass unit in a variety of configurations (one, two or three coated films, uncoated or low-E coated glass) to achieve energy savings ranging from R-6 to R-20 in order. meet the unique requirements of commercial and residential new construction and renovation. The marking contains a two-digit number that represents the amount of light passing through the coated film. For example, Heat Mirror™ 22 is designed to block more infrared light than Heat Mirror™ 88.

The polyester film bisects a layer of argon or krypton gas that fills the gap between the two panes of glass, creating an additional air space that greatly improves the window's R-value and associated heating and cooling costs. Inspectors and homeowners can be confused about the properties of Heat Mirror™ and other eco-friendly products commonly used on windows, such as low-E coatings, which also use a reflective layer to reflect infrared energy.

Low-E Film

Low-E film, however, is made of metal or metal oxide instead of polyester and is physically applied to the surface of the glass. Unlike Heat Mirror™, the low-E coating does not increase the number of air gaps in the IGU.

The debate over which is the better design has gone on for many years, with proponents on both sides pointing out the flaws and inefficiencies of the other product. These two designs are sometimes incorporated into the same IGU for additional protection against thermal or infrared energy loss.

Amory Lovins is a Colorado resident who, according to MSN Money, pays $0 in energy bills for one of the greenest homes on the planet. Heat Mirror™ and other energy-saving features enabled 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 every winter experiences sub-zero blizzards. As part of the building's energy retrofit project, Heat Mirror™ is also planned to be installed in 6,500 windows of the Empire State Building. According to BusinessWire , installing Heat Mirror™ in the windows of New York's tallest building will reduce energy costs by $400,000, cut solar heat gain in half, and improve the windows' R-value from R-2 to R-8. Skyscrapers and alpine banana jungles aside, most Heat Mirror™ window films are found in common residential and commercial structures, although they are among the more expensive options available.

LiteHouse Commercial inspectors may look for older types of Heat Mirror™ that are prone to discoloration, warping, embrittlement and seal failure. One such defect is yellowing caused by impurities that get on the film before it is fused to the glass panes. Wrinkling is also a problem with older Heat Mirror™ as you can see in the attached photo. These issues have largely been resolved in recent years as Southwall has corrected manufacturing defects and more thoroughly investigated its licensed distributors.

In short, Heat Mirror™ and other types of window film are designed to reflect solar heat, increase the window's R-value, and/or provide shading while reducing a building's energy costs for both heating and cooling, sometimes significantly, depending on the product.

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