DOE High Performance Windows and Low-E Storm Windows Volume Purchase Program
For those interested in maximizing heating energy savings through window energy efficiency, the U.S. Department of Energy (DOE) started the Highly Insulating (R-5) Windows and Low-E Storm Windows Volume Purchase Program in 2010. This program connects potential buyers with vendors of highly insulating windows and low-E storm windows by allowing buyers to check out available product options and price ranges at www.windowsvolumepurchase.org. While DOE does not offer any incentives for purchases through this program, the web platform encourages competitive pricing among the participating vendors, and the program's qualification criteria ensure that the listed windows and storm windows offer superior insulating performance.
High Performance Windows
To qualify for the volume purchase program, windows must meet these criteria:
- U-factor 0.22 or less for operable windows, 0.20 or less for fixed windows
- Must be NFRC-certified
- Air leakage 0.30 cfm/ft2 or less
- 20 year warranty for the glass package, 10 year warranty for the window
- R-25 Performance Grade or higher established under the AAMA/WDMA/CSA 101/I.S.2/A440 (NAFS) standard
Compares to a U-factor of 0.35, which is typically required by building energy codes in heating-dominated climates, a U-factor of 0.22 represents a significant reduction in window heat loss.
Low-E Storm Windows
To qualify for the volume purchase program, storm windows must feature heat-reflective low-E glass, a 10 year warranty, and a Performance Grade of 15 or higher established under the ANSI/AAMA 1002.10 standard.
Storm windows improve the insulating value and reduce the air leakage of windows. If installed over a single-pane window (whether on the interior or exterior), a storm window can reduces heat loss by 25-50 percent. Even greater savings can be achieved if the storm windows have low-E glass, which reduces radiative heat transfer from warm to cold surfaces. The additional cost of low-E glass is relatively minor compared to the heating savings impact, and a 2006 field study by HUD's Partnership for Advancing Technology in Housing (PATH) suggests that use of low-E glass reduces the payback period for storm windows in heating-dominated climates.
One potential issue to keep in mind is that storm windows can trap moisture between them and the original windows. To prevent condensation, air leakage from the indoors into the window/storm window gap should be minimized, while venting from the gap to the outdoors should be allowed (e.g. through weep holes).