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Installing a window film or adhesive coating can boost the efficiency of your current windows by reflecting sunlight and reducing its transmission into your home or office as heat; some films also insulate against interior heat loss. Window films offer one of the most cost-effective and least labor-intensive ways to decrease energy loss through your windows.

How to choose a window film

  • Select the film best suited to your needs; consider whether you will need a film designed to reflect sunlight or one that retains interior heat.
  • Decide on an installation procedure: while many films can be self-installed by carefully applying them to interior glass surfaces, professional installation is recommended in most cases to ensure adequate sealing and aesthetics.
  • When applying a film yourself, do so in the early morning or late afternoon to avoid problems associated with exposure to excessive heat during the initial application.[1]
  • If using a removable film, make sure to take it off the window during colder seasons as needed to benefit from incoming solar radiation.

Find It! Window films

Choosing window films helps you go green because…

  • Window films reduce solar heat gain, thereby decreasing a home's cooling energy consumption on hot days.
  • They provide increased insulation against heat escape through windows in colder climates.
  • They can reflect the ultraviolet radiation that often fades and damages carpets and furniture.
  • Films can act as a protective reinforcing layer, preventing scratches to the surface glass and reducing the chances that a window will shatter if broken.
  • They can reduce solar glare while increasing privacy.
  • Many films boost window efficiency without obscuring exterior views.

Windows and doors contribute up to 30 percent of heat loss and gain in a home, by direct conduction through the glass and via air leakage through the window assembly.[2] The US Department of Energy (DOE) estimates that heat loss and gain through today's windows account for approximately 4 percent of total domestic energy consumption.[3] Efficiency strategies vary widely based on regional climate considerations: windows can account for 25 percent of of a typical home's heating energy load in cooler climates, and as much as 50 percent of the cooling load for homes in warmer climates.[4] Windows cover between 10 and 25 percent of the exterior surface area in new homes and selecting windows designed to either retain or repel heat is an important aspect of a whole-house energy efficiency plan. The DOE advocates reducing the environmental emissions from heating and cooling systems—some 150 million tons of CO2 alone annually—from 20-50 percent.[5]

How do window films work?

While window films can serve a variety of purposes, they primarily act as a barrier of resistance against solar heat gain, both reflecting and absorbing sunlight at higher rates than uncoated glass and thus reducing cooling energy consumption on hot days; many films can also act as an added layer of insulation to minimize heat loss during colder seasons.[1] Usually composed of thin plastic or polyester, window films can either be applied directly to a window's interior pane by consumers or else must be glued into place by professional installers.[6] Tinting, reflective coatings, and spectrally-sensitive low-emissivity treatments are the most common technologies used to limit heat transfer.[7] Because tinted window films contain pigments or dyes that absorb—rather than reflect—all wavelengths of light (visible, infrared, and ultraviolet), they tend to radiate more heat inside the home while admitting less light than other window films,[7] often increasing energy consumption associated with artificial lighting.[8] Reflective films employ a metal oxide coating that more effectively blocks sunlight from entering the home, but often create a shiny mirror effect when viewed from the outside during the day and from the inside at night.[9] Spectrally sensitive low-e window films permit certain parts of the solar spectrum-like visible light-to pass through while blocking others.[10] These low-e films use special metallic coatings which can be customized for the heat resistance or retention priorities of homeowners in different climates.

How effective are window films?

Some window films can reflect as much as 70-80 percent of the solar heat that would otherwise pass through a window pane,[11] while others can retain approximately 55 percent of interior heat.[1] Protection rates against ultraviolet radiation are commonly as high as 99 percent.[12] While actual reflection and retention performance varies according to regional climate considerations, checking a window film's solar heat gain coefficient (SHGC) and visible transmittance rating (VT) should supply the information necessary to determine whether a window film is appropriate for a given situation. Colder climates generally benefit from products with a high SHGC, while hot climates are better suited to low SHGC window films.[13] The higher the VT rating, the more light a window film admits, so consumers considering natural daylighting or those seeking interior shade can adjust their selections accordingly.

Tax breaks and subsidies

In the US, installing window films may qualify you for tax incentives at the federal, state, or local levels. For detailed information, see these resources:

What are the drawbacks?

  • Manufacturers of some double-pane windows will void their warranties on windows that have been retrofitted with a film, due to the added heat expansion that sometimes occurs in the interior pane.[14] Reading the fine print on window warranties-in conjunction with any separate warranties associated with a window film itself-should offer protection to consumers against limiting conditions.[8]
  • Tinting films have the potential to block out so much light that the added energy burden from electric lighting may diminish any savings the such films provide.[14]
  • Some homeowner's associations may restrict windows that appear overly shiny and mirror-like from the outside, often a side-effect of highly reflective window films during the day, and one that may likewise be visible from the inside looking out once night falls.[14]
  • Window films do have the potential to harm certain houseplants that require extensive sunshine in order to thrive indoors. Houseplants that hold up poorly when removed from direct sunlight for any considerable length of time may likewise suffer from the reduced sunlight that passes through a window film with low visible transmittance properties, and should be relocated accordingly.[15]

Glossary

  • visual transmittance value (VT): A measurement indicating the percentage of the visible light spectrum that is transmitted through a given glazing or pane.[16]
  • light-to-solar-gain ratio (LSG): A ratio comparing the light admitted vs. heat transmitted by a window glazing or film, measured in terms of the visual transmittance and solar heat gain coefficient.[17]

External links

Comments

08/13/2009
7:18pm
jn1009

Could you add a low E film to your front and rear car windows to prevent it from getting so hot in the summer? I don't think the film could stand up the constant friction of being rolled up and down on the side windows.

08/13/2009
7:48pm
greengoddess

I've not personally, but i know a couple people that have ... here is video showing one method of doing it, though have to say, not sure its the greenest technique out there!!! http://www.monkeysee.com/play/13390-tint-car-windows-heat-shrinking-the-rear-window

09/07/2009
12:24pm
judy

Is it o.k. to use Gila heat reflective film on the top 1/4 part of a thermal store window? Why can't it be used on thermal windows? How do I know if our store window is thermal glass? Thank you

09/07/2009
9:15pm
greengoddess

here is a good place to start to answer part 2 of your Q. scroll down the page to see info on thermal windows......http://en.wikipedia.org/wiki/Thermal_window

01/30/2010
10:05pm
davidftg

Any opinions on the relative benefits of v-Kool, 3M Prestige, and Spectrally Selective Vista?

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