Interior low-e panels were installed at 400 Market Street, a 12-story office building in Philadelphia, Pennsylvania. 400 Market Street experienced significant energy savings as a result of the secondary glazing system retrofit, including 25% whole building heating and cooling energy savings, as well as improved comfort and decreased street noise.

This field evaluation compared the performance of low-e storm windows with clear storm windows and no storm windows in six Chicago homes with single pane windows. Overall heating load reduction due to the storm windows was 13% with the clear glass and 21% with the low-e windows. Simple paybacks for the addition of the storm windows were 10 years for the clear glass and 4.5 years for the low-e storm windows.

Center for Energy and Environment (CEE) partnered with Xcel Energy and Pacific Northwest National Laboratory (PNNL) to evaluate interior storm windows as an energy savings measure. Funding for this field testing was provided in part by the Department of Energy to develop cost-effective energy saving technologies. The home was selected through an energy audit as a candidate that could benefit from storm window improvement. New interior storm windows were installed in the home, which had old and leaky exterior storm windows estimated to be 30–50 years old.

In this case study, clear glass storm windows were replaced with low-e storm windows and evaluated on two large three-story residential multifamily apartment buildings in Philadelphia. This retrofit resulted in 18-22% reduction in heating use, 9% reduction in cooling use, and a 10% overall reduction in apartment air leakage.