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Benefits of Low-E Window Glazing vs. Quad-Glazing using Sungain Film
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Which type of energy-efficient window glazing is better: low-E glass or quad-glazing using 2 layers of Sungain film for sunspace or greenhouse windows?
Matching type of energy efficient window glazing to room type and use
Optimizing window glass for comfort vs. solar gain
Optimizing window glazing for heat producing sunspace - solar heating
Specifications of low-e glass
Questions & answers about types of Low-E window glazing
Solar Age Magazine Articles on Renewable Energy, Energy Savings, Construction Practices

This article compares the benefits and differing applications for low-e window glazing versus Sungain type window film coatings and explains different applications in which each type of product is likely to be more satisfactory.

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Readers should also see SUNGAIN, FILMS, LOW-E GLASS for details about use of Sungain film on windows and window film selection and installation, and see WINDOWS & DOORS our home page for window and door information. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

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Comparing Energy Efficiency of Low-E Glass vs Quad Glazing

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

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A window salesperson suggested to me that triple glazing with low-emissivity (low-e) glass would be better than quad glazing (two layers of 3M Sungain film) for sunspace (or greenhouse) windows.

He maintained that the low-e window units would make the room feel warmer because it would reflect the long-wave radiation (heat) back into the room.

Which window glazing product, low-E glass or 3M Sungain films, would be better for this application? - Roger Saunders, Hollis NH

Answer: It Depends ...

The answer to the question of which window glazing approach will perform better depends on the type of room and its intended use, according to H. J. Koester of Weather Shield, a company that makes both types of window glazing.

Choosing Window Glazing for Optimum Comfort

If the sunspace is a direct extension of the living area and comfortable sitting conditions are of greater importance than solar gain, he suggests that the low-e glass would be a better value due to its higher R-value and lower cost.

Our photo above-left shows a very high-gain passive solar home in San Miguel de Allende, Mexico. This could have been an installation where comfort weighed more heavily than the need for optimizing for solar heat.

Choosing Window Glazing for Optimum Solar Gain - Solar Heating

For a heat-producing sunspace, he says that the quad glazing approach with Sungain film would be a better approach, because of its higher solar transmittance and small sacrifice in R-value.

Efficient Window Glazing Specifications

Weather Shield's Triple Low-e glass has a solar transmittance of 0.52 to 0.55 and an R-value of 4.34 (for the 1 1/2-inch unit).
For quad glazing, the transmittance is 0.63 and the R-value is 3.85.
While the quad-glazed (Sungain film) window is a better solar performer, it is also more expensive by 10-20 percent (1985 prices - check current numbers- Ed).
As in all window glazing decisions, it boils down to a series of tradeoffs.
Weather Shield's Low-e glass is the hard-coat type, imported from Belgium. Its performance measures may not apply to comparable U.S.-made window glass.

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

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

Comparison of Window Type Energy Efficiencies¹
Window Type	U-Value²
Single-glazed standard glass	1.13
Double-glazed, 1/2" air space	0.56
Triple-glazed, 2 1/2" air spaces	0.34
Low-E, double glazed, 1/2" air space	0.33
Heat Mirror, double glazed, 1/2" air space	0.23

1. Popular Science Magazine in 1982

2. U-value is the measurement of heat transmission through a material - it's the reciprocal of R-value. R-value is a material's resistance to heat transfer.

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

Original article

Q&A: Performance Comparison of Low-E vs. Quad Glazing - Sungain Window Films - PDF version; use your browser's back button to return to this page. Original article, Solar Age Magazine, October 1985, adapted and updated for InspectAPedia.com December 2010.

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Questions & answers about types of Low-E window glazing.

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  LOW-E WINDOW GLAZING
  LOW-E VS QUAD-GLAZING
  LOW-E RETROFIT ADD-ON FILMS

Solar Age Magazine was the official publication of the American Solar Energy Society. The contemporary solar energy magazine associated with the Society is Solar Today. "Established in 1954, the nonprofit American Solar Energy Society (ASES) is the nation's leading association of solar professionals & advocates. Our mission is to inspire an era of energy innovation and speed the transition to a sustainable energy economy. We advance education, research and policy. Leading for more than 50 years. ASES leads national efforts to increase the use of solar energy, energy efficiency and other sustainable technologies in the U.S. We publish the award-winning SOLAR TODAY magazine, organize and present the ASES National Solar Conference and lead the ASES National Solar Tour – the largest grassroots solar event in the world."
Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education. Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com.
Excerpts with updates and annotations expanding the original Best Practices Guide text can be found in the online review and book summary at BEST CONSTRUCTION PRACTICES GUIDE and also at DECK & PORCH CONSTRUCTION, at INDOOR AIR QUALITY IMPROVEMENT GUIDE, and in other articles found at InspectAPedia.com such as HOUSEWRAP AIR & VAPOR BARRIERS, SOUND CONTROL in buildings, and other topics.
3M Corporation, 3M Energy Control Products Project, Building 224-5S, St. Paul MN 55144 [1980's]
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. Thanks to Alan Carson and Bob Dunlop, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education including the ASHI-adopted Home Inspection Training Program (home study course), publications such as the Home Reference Book, report writing materials including the Horizon report writer, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
Passive Solar Design Handbook Volume I, the Passive Solar Handbook Introduction to Passive Solar Concepts, in a version used by the U.S. Air Force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v1.pdf
Passive Solar Design Handbook Volume II, the Passive Solar Handbook Comprehensive Planning Guide, in a version used by the U.S. Air Force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v2.pdf [This is a large PDF file that can take a while to load]
Passive Solar Handbook Volume III, the Passive Solar Handbook Programming Guide, in a version used by the U.S. Air Force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v3.pdf
The Passive Solar Design and Construction Handbook, Steven Winter Associates (Author), Michael J. Crosbie (Editor), Wiley & Sons, ISBN 978-047118382 or 0471183083 is available at Amazon.com and via the The Passive Solar Design and Construction Handbook, Steven Winter Associates (Author), Michael J. Crosbie (Editor), Wiley & Sons, ISBN 978-047118382 or 0471183083 is available at Amazon.com and via the InspectAPedia Bookstore
"Passive Solar Home Design", U.S. Department of Energy, describes using a home's windows, walls, and floors to collect and store solar energy for winter heating and also rejecting solar heat in warm weather.
"Solar Water Heaters", U.S. Department of Energy article on solar domestic water heaters to generate domestic hot water in buildings, explains how solar water heaters work. Solar heat for swimming pools is also discussed.
"Heat Exchangers for Solar Water Heating Systems", U.S. DOE describes the types of solar water heater heat exchange methods between the sun and the building's hot water supply
"Heat-Transfer Fluids for Solar Water Heating Systems", U.S. DOE, describes the types of fluids selected to transfer heat between the solar collector and the hot water in storage tanks in a building. These include air, water, water with glycol antifreeze mixtures (needed when using solar hot water systems in freezing climates), hydrocarbon oils, and refrigerants or silicones for heat transfer.
"Solar Water Heating System Maintenance and Repair", U.S. DOE
"Solar Water Heating System Freeze Protection", U.S. DOE,using antifreeze mixture in solar water heaters (or other freeze-resistant heat transfer fluids), as well as piping to permit draining the solar collector and piping system.
"Scaling and Corrosion in Solar Water Heating Systems", U.S. DOE
www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12850 is the base U.S. DOE website for these articles
"Active Solar Heating Systems", U.S. Department of Energy, including
"Radiant Heating Systems" U.S. DOE
"Absorption Heat Pumps & Coolers", U.S. DOE
"Solar Air Heating" U.S. DOE also referred to as "Ventilation Preheating" in which solar systems use air for absorbing and transferring solar energy or heat to a building
"Solar Liquid Heating" U.S. DOE, systems using liquid (typically water) in flat plate solar collectors to collect solar energy in the form of heat for transfer into a building for space heating or hot water heating. The term "solar liquid" is used for accuracy, rather than "solar water" because the water may contain an antifreeze or other chemicals.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com.
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Comparing Energy Efficiency of Low-E Glass vs Quad Glazing

PVC Vinyl Window Warping Q&A

Question: What are the facts about the occurrence of shrinkage and warping in PVC or Solid Vinyl Windows?

Answer: It Depends ...

Choosing Window Glazing for Optimum Comfort

Choosing Window Glazing for Optimum Solar Gain - Solar Heating

Efficient Window Glazing Specifications

Original article

Questions & Answers regarding this article

Ask a Question or Search InspectAPedia

Technical Reviewers & References

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair