A report titled, "Saving Windows, Saving Money: Evaluating the Energy Performance of Window Retrofit and Replacement," concludes that upgrading windows (specifically older, single-pane models) with exterior storm windows and insulating shades can result in substantial energy savings across a variety of climate zones.
The study was commissioned by the Preservation Green Lab and funded by The National Park Service's National Center for Preservation Technology and Training.
It analyzes decades of research about the performance of double hung windows, comparing the relative energy, carbon and cost savings of various choices in multiple cities across the United States.
"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," said 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."
These findings have important environmental and economic ramifications for consumers. Residential buildings are responsible for approximately 20% of total U.S. energy use and carbon dioxide emissions. Many of these buildings are single-family homes where heating and cooling represent the largest uses of energy, and where windows are an important factor in home energy efficiency. Americans spend over $17 billion annually on heating and cooling.
"Homeowners and designers who want to upgrade existing windows have many choices: from simple, low-cost, do-it-yourself solutions to complete replacement, which can cost tens of thousands of dollars," said David Brown, executive VP and chief preservation officer of the National Trust for Historic Preservation. "This report provides the context and data to help budget conscious consumers make sound decisions."
Research support for the study was provided by Cascadia Green Building Council and Ecotope, a consultancy focused on energy efficiency and sustainability.
The full report and an overview of key findings are at preservationnation.org/saving-windows-saving-money.