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Project Launch: 08/01/2021

Partners: Slipstream, Nicor

This project was a collaboration between utilities that assessed the existing secondary glazing system market and determined the growth potential for this technology.


Secondary Glazing Systems (SGS) are window attachments with insulating high-performance glazing in anodized or painted aluminum frames with low-e coating on double-lite glass. With an estimated 20% savings over a typical single-pane window, the total market savings potential in ComEd's service territory is approximately 13.8 GWh, assuming full market saturation.

Despite improvements in window technology, the SGS market is still small in northern Illinois. There remain significant barriers to substantial growth in sales of secondary windows in ComEd’s service territory. A combination of market research, quantitative analysis and stakeholder engagement was used to fully understand these barriers. After assessing the existing SGS market, the project team focused on determining what market interventions would be most impactful and whether this measure is best suited for program deployment or market transformation.

Results and Outcomes

Secondary glazing systems showed significant savings potential in heating dominated climates such as ComEd’s service territory. Data collected in this study from simulation and field tests, manufacturer and customer interviews all indicated positive energy savings and improved user experience from SGS retrofits. Savings varied significantly based on the characteristics of the existing building but are estimated to offer a 10-30% reduction in total energy use. Field studies showed that SGS retrofits can save 7.6 kBtu/sf and 15.1 kBtu/sf whole building energy savings from a single pane and double pane SGS retrofit, respectively. This translates to $0.09/sf energy cost savings.

SGS also results in significant non-energy benefits such as an increase in thermal comfort, noise reduction, glare control, etc. However, technology awareness is a key barrier to higher SGS adoption. Customers are largely unaware of this technology and default to window replacements for improving envelope performance.

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