Adding low-Emissivity film coatings to windows: this article describes low-e window films that can be added to existing windows to improve window efficiency and improve solar gain in cold weather.

Compare Energy Efficiency of Low-E Glass vs Quad Glazing: Add-on films for low-e energy-efficient window glazing, Low-e window films for upgrading existing windows, Winter films and all-weather films retain indoor heat in cold weather, Low-e coated films for inside storm windows.

Questions & answers about using add-on or retrofit films to improve window energy efficiency. Solar Age Magazine Articles on Renewable Energy, Energy Savings, Construction Practices.

Comparing Energy Efficiency of Low-E Glass vs Quad Glazing

The text below is reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss. Photos by Daniel Friedman.

Low-e Window Retrofit Film Products for Existing Windows

Two low-e window films and one inside storm window were available in the mid 1980's and more such products are currently provided by several manufacturers.

The add-on or "retrofit" low-e window films are applied to the inside of the window glass with a squeegee, using water as the adhesive. These "winter films" or "all-weather" films are tuned to retain winter heat and reject some outside heat gain.

They probably make the most sense as window energy improving retrofits in houses located north of the Mason-Dixon line.

Scotch-tint Plus All Season claims to reduce heat gain by 60 percent and wintertime heat loss through the window by 40 percent.

It also blocks 98 percent of UV light that fades indoor furnishings. Scotch-tint is available from 3-M Co., St. Paul MN.

The second low-e retrofit window film is Gila River Products' [Chandler AZ] PWD-5 with roughly similar characteristics to the 3-M Scotch-tint film.

With a winter U-value of .85, this film ups the R-value of a single pane 1/8-inch thick window [glass] from around .90 to 1.18, a 31 percent improvement in window efficiency.

What is lost when a low-e film like these is applied to a window is some useful solar gain and light in winter, due to the film's low transmittance (0.55).

To our knowledge, the only low-e retrofit storm window is the Windo-Tite unit. It is an aluminum-framed single window that attaches to the inside of the primary window via swivel clips or sash locks. It has a tested U-value of .408 (r-2.45 for storm plus primary window). Amesbury Industries, [Amesbury MA] supplies the glazing frames and accessories to local distributors who make up the window units.

The question-and-answer article above paraphrases, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.

This article is reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

For more up to date information about the performance of films to increase solar collector efficiency,

see SOLAR COLLECTOR FILMS

and SUNGAIN, FILMS, LOW-E GLASS for details about use of Sungain film on windows and window film selection and installation.

A wide range of energy conservation and solar energy topics is found

at SOLAR ENERGY SYSTEMS. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

Definition of Window Coating or Film Emissivity & Typical Emissivity Numbers for Low-E Films & Coatings

Window glazing may be factory-coated or as this article describes, an add-on adhesive low-e (low emissivity) film may be adhered to the inside or outside window surface (or both).

The emissivity of a window is a measure of its insulating performance expressed as the percentage of near-to-the-window infra-red heat in a room that is reflected back into the room (reducing heat loss from the building to outdoors), or from outside, the percentage of near infra-red-heat that is reflected back away from the window surface (reducing heat gain through the window and into the building).

• A window film emissivity of 0.07 means that 0.93 or 93% of the room's nearby infra-red heat is reflected back into the building interior - signifiantly reducing winter heating costs, depending on what other building heat loss prevention measures have been taken. See our Watch Out note below.
• A window film emissivity of 0.33 means that 0.67 or 67% of the room's nearby infra-red heat is reflected back into the building interior
• A window film emissivity of 0.70 means that 0.30 or 30% of the room's nearby infra-red heat is reflected back into the building interior.
• A window film emissivity of 0.81 means that 0.19 or 19% of the room's nearby infra-red heat is reflected back into the building interior.

In short, lower emissivity numbers mean more IR heat reflection (less heat is emitted through the window glazing) back into the occupied space. There are currently two low-e film performance ranges, depending on what product you buy.

Conventional low-e window film 

has a typical emissivity rating of 0.33, reflecting 0.67 or 67% of the near infra-red heat in a room back into the room interior. This film will improve the energy efficiency of a conventionally-glazed window by about 44% with the warnign that some low-e window films may produce a distracting irridescent or shiny surface dependign on the type of interior lighting used. Compact fluorescent bulbs tend to produce this irridescent sheen.

High performance low-e window film

 has extremely-low emissivity ratings, down as low as 0.07, reflecting 0.93 or 93% of the nearby infra-red heat back into the building interior. Expert sources we reviewed claimed a window insulating performance improvement of "up to" 92%.

Watch out: the energy savings potential of adding low-emissivity window films or buying low-e replacement windows or installing low-e windows in new construction will be limited if other building heat loss (or in hot climates un-wanted heat-gain) measures are not taken.

For example, if there are signficant air leaks in the building or if the building wall and ceiling or roof insulation blankets are incomplete, the energy costs of those defects are likely to overwhelm any potential benefit of low-emissivity films or coatings on windows.

See ENERGY SAVINGS PRIORITIES

Sources of Low-E Add-On or Stick-On Window Films & Window Film Detection Instruments

• 3M Outdoor Window Insulator Kit, Two Pack, 2170 W-6, Product ID: 3M 2170 W-6 UPC: 00-051141-32384-8, 00051141323848 Stock ID: 70-0050-7990-3, 70005079903, available from re-sellers, this is a current version of Scotch Tint window films discussed by Steve Bliss in the article above. To review the differences among six different 3M™ window film products see the window film manual below.
  
  Scotchtint™ / Scotchshield™ Window Film Manual [PDF], 3M™ Corporation, 2003. Abstract quoted from this window film selection & installation guide:
  
  Patented window films that improve comfort and cut energy costs by reducing heat loss and solar heat gain through windows. The films can improve aesthetics by providing uniformity to the exterior appearance of windows, while not impairing the view.
  
  Other benefits include reduction of UV damage to interior materials, reduced temperature imbalances between sunny and shady ares of the building, improve glass safety and increased daytime privacy. 3M Consumer Safety and Light Management Department 1-800-480-1704
• Building suppliers such as Lowes and Home Depot are retailers of several low-E window films
• EDTM Double Pane Low E Coating Detector, Part Number: AE1601, about $300. U.S.D., product description excerpt:
  Confirm the invisible Low E coating is properly installed into your double pane IG units with a single test from a single side. You can also test a triple pane window by testing both sides of the window. For full triple pane Low-E detection, see the Glass-Chek PRO.
• EnerLogic® low-e window film, Website: http://www.enerlogicfilm.com/products, Excerpt from product description: EnerLogic® low-e window film reduces solar heat gain and radiant heat loss, creating year-round heating and cooling savings of up to three times as much as conventional window film with comparable light transmission. - See more at: http://www.enerlogicfilm.com/products#sthash.okXs1CCh.dpuf
  
  In Australia contact EnerLogic at: 275 Canterbury Road, Canterbury VIC 3126 Free Call: 1800 134 776
  In New Zealand contact EnerLogic at: 24A Tarndale Grove,Albany, Auckland 0632 Free Call: 0800 134 776
• Gila 36-in W x 180-in L Platinum Heat-Control Adhesive Window Film Item #: 23153 | Model #: LES361, widely sold online and at building suppliers
• Hanita Pacific Pty Ltd Unit 4, 50 Rooks Rd Nunawading VIC 3131 Australia Tel: 1300 456 700 Fax: 1300 456 600 info@hanitapacific.com.au Website: http://www.hanitacoatings.com/ selling low-e films in Australia & New Zealand
• Solar Guard Saint Gobain, [Dream on if you hope to find actual contact information such as a mailing address for this company - Ed.] "Solar Gard window film products. For more information, please contact Customer Service at
  1800 251 575 or fill out the form [at http://www.solargard.com/] " markets low-e films in Australia and other countries.
• SolarShield, U.K. low-e window coatings and films, Solarshield Limited Canada House 20/20 Business Park St Leonards Road Maidstone Kent ME16 0LS Email: info@solarshield.co.uk Phone Number: 0845 130 6232 Local Rate Phone No: 0162 275 4660
• Madico window films, coatings, laminates, Madico Window Films 2630 Fairfield Ave. South St. Petersburg, FL 33712, Website: http://www.madico.com/, Excerpt from the company's description:
  
  Madico is a world leader in the COATING, LAMINATING, and CONVERTING of films in wide width, roll-to-roll format. Our products are multilayered, engineered films primarily targeting applications in Energy-related markets such as Solar Control Window Films, Photovoltaic Backsheets, and Safety/Security Films.

As we discuss in more detail at SUNGAIN, FILMS, LOW-E GLASS, here is a quick comparison of window types and their efficiencies:

• Q&A: Low-e Retrofit Products - Window Films - PDF version; use your browser's back button to return to this page. Original article, Solar Age Magazine, September 1986, adapted and updated for InspectAPedia.com in 2011.
• Q&A: Low-e Retrofit Products - Window Films-page2 - PDF version; use your browser's back button to return to this page. Original article, Solar Age Magazine, September 1986, adapted and updated for InspectAPedia.com in 2011.

...

Continue reading at WINDOW EFFICIENCY FEATURES & RATINGS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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LOW-E RETROFIT ADD-ON FILMS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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