Repairing a home’s older windows delivers similar energy benefits as compared to replacing them with high-performance windows, and it can be done at less cost, according to a new study from the Preservation Green Lab. “Saving Windows, Saving Money: Evaluating the Energy Performance of Window Retrofit and Replacement” was funded by the National Park Service’s National Center for Preservation  Technology and Training.

The study analyzed research regarding the performance of double hung windows and compared the relative energy, carbon, and cost savings of various choices in various climate zones. The report concludes that upgrading windows—specifically older, single-pane windows—with exterior storm windows and insulating shades can result in substantial energy savings in multiple climate zones, according to the National Trust for Historic Preservation. The study examined data from Atlanta, Boston, Chicago, Phoenix, and Portland, Ore.

“A number of existing window retrofit strategies come very close to delivering the energy benefits of high-performance replacement windows–at a fraction of the cost,” says Mark Huppert, technical director of the Preservation Green Lab. “From weather stripping and sealing, to installing exterior storm windows or interior cellular shades, almost every retrofit option offers a better return on investment than outright replacement.”

Key findings of the report include:

  • Retrofit measures can achieve similar performance results as compared to new replacement windows. Specifically, interior window panels, exterior storm windows combined with cellular blinds, and, in some cases, exterior storm windows alone fall within the performance range of replacement windows. 

  • For all five cities, cost analysis shows that new, high-performance windows average approximately $30,000 for materials, installation, and general construction commonly required for an existing home. In comparison, the study asserts that in cold climates all other retrofit measures with the exception of weather stripping and heat-reducing surface films offer a higher average return on investment. In hot climates, the study asserts that all retrofit measures with the exception of weather stripping offer a better average return on investment than new windows. 

  • Rates of return for window retrofit measures ranged from 3 percent to 4 percent for most regions studied.

The study used computer simulation to model energy use in a typical, prototype home before and after window improvements. Commercially available window improvement options ranging from low-cost solutions to more expensive options were analyzed. Energy, cost ,and carbon savings were examined in seven specific measures: weather stripping existing windows; interior window panels; exterior storm windows; insulating cellular shades; a combination of exterior storm windows and insulating cellular shades; interior-applied surface films; and new, high-performance replacement windows.

The full report is available for download at preservationnation.org/saving-windows-saving-money.