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What is a high-performance window?

What is a high-performance window?

High-performance windows (HPWs) are low U-factor (equivalent to high R-value) fenestration products used in single- and multifamily homes and some commercial buildings. These are defined as windows that meet the ENERGY STAR Version 7 criteria and have a U-factor of 0.22 or lower. Window technology has advanced over the years from the original fixed single-pane window to operable assemblies that include multiple panes and individual components to improve the product’s thermal performance.  

Until recently, ENERGY STAR certification of windows, doors, and skylights has been defined in northern climates as a window with a U-factor of 0.27. Today, ENERGY STAR Version 6 windows make up a significant portion of the market and typically take the shape of a double-pane window with a low-emissivity — or “low-e” — coating. Technology advances in recent years have created multiple pathways for manufacturers to achieve even higher-performing window products including high-performing, low-e double-pane windows and thin, hybrid, or standard triple-pane windows.  

Benefits of high-performance windows

These products improve the energy performance of a building by improving the envelope’s thermal insulation, air leakage, and solar heat gain components to optimize HVAC performance. These products also offer an impressive array of non-energy benefits including improved comfort, noise reduction, and health benefits from reduced condensation. 


Why we’re working to advance the adoption of high-performance windows

Windows are the least efficient element of the building envelope, and as the nation moves to decarbonize its buildings, it will be imperative to improve this weak link. Despite making up only 8% of a typical home’s building envelope area, windows account for 45% of envelope heat transfer. Improving homes’ thermal envelopes should have symbiotic effects on mechanical systems within homes. 

Better envelopes will allow for smaller HVAC and heat pump systems, which will maximize their effectiveness, reduce operational costs, and minimize grid impacts of electrified heating loads. And because windows can last up to 45 years, decisions made today will have generational impacts.