Recently, the U.S. Environmental Protection Agency’s (EPA) ENERGY STAR^® program released its final specification (Version 7.0) for residential windows, doors, and skylights that establish higher energy-efficiency benchmarks for products to earn EPA’s coveted ENERGY STAR certification. The new Version 7.0 performance specifications were many years in the making and built upon research and development from DOE’s Building Technologies Office (BTO) and Lawrence Berkeley National Laboratory (Berkeley Lab).

The energy performance of windows is essential to overall building efficiency and its environmental impact. More efficient windows will reduce your home’s carbon emissions on day one, independent of what source of energy is used to heat and cool your building. Although windows only account for about 10% of an average home’s surface area, approximately 35% to 45% of the heat homes lose in winter months pass through windows. More insulative windows, like the industry-leading models that the new ENERGY STAR criteria will certify, can bring those losses down considerably, which saves money, energy, and emissions of carbon dioxide from entering the atmosphere and exacerbating the climate crisis.

BTO’s Emerging Technologies and Residential Buildings Integration programs funded and conducted a significant share of the market and technological analyses EPA used to establish fair, yet ambitious, targets for the energy performance of ENERGY STAR windows, doors, and skylights. For years, BTO has pursued the long sought-after goal of achieving market viable triple pane performance, which will be a key design feature of many windows meeting the Version 7.0 criteria.

EPA’s ENERGY STAR V7 specifications were analyzed and modeled with Berkeley Lab’s suite of energy performance software tools. Its Berkeley Lab WINDOW tool helps calculate total window thermal performance indices, which manufacturers widely use to develop new window designs while optimizing cost and performance trade-offs. And some of the latest window products on the market today that meet V7’s specifications, like thin-triple-paned windows, were initiated and developed by Berkeley Lab in collaboration with industry with BTO support. Unlike traditional two-pane windows, “thin-triples” add a third pane of glass, creating two insulated air pockets along with two low emissivity coatings that improve window energy performance by 40% or more. Thin-triples offer reduced weight compared to conventional triples, and consumers consistently praise triples for another kind of insulation – sound insulation. Some studies have found that thin-triples can cut the perception of outside noise in half.

Now, ENERGY STAR’s V7 specifications are expected to result in dramatic increase in triple-pane window sales in the northern part of the country. The new specifications are also expected to foster innovation with some companies starting to pursue industry-leading thin triple-pane glass processing equipment that will only have one spacer vs. two, which should further reduce cost and improve reliability.

To build on BTO’s efforts to research and improve the market adoption of window products like these that save energy, DOE launched the Partnership for Advanced Window Solutions (PAWS) in May 2021, as part of BTO’s Initiative for Better Energy, Emissions, and Equity (E3 Initiative). For over a year, BTO, DOE national labs, and the Northwest Energy Efficiency Alliance have been working with builders, utilities, efficiency advocates, and manufacturers to both drive demand and scale up production of cost-effective triple-pane window designs and other high-performance window solutions. BTO also published a new roadmap that outlines multiple avenues for further technology development, deployment, and adoption to increase the impact that high-performance windows can have on decarbonizing buildings.