Energy Star Windows – Criteria for Energy Efficient Windows

Replacing your windows with Energy Star windows is one of the best ways to make your home more energy efficient. Learn more in this video:

An Energy Star qualified window is independently certified and tested by the National Fenestration Rating Council (NFRC), has NFRC ratings that meet the U.S. Department of Energy’s strict energy efficiency guidelines, and is manufactured by an Energy Star partner.

The Energy Star Program defines a “window” as an assembled unit consisting of a frame/sash component that holds one or more pieces of glazing functioning to admit air and/or light into an enclosure and designed for vertical installation in an external wall of a residential building. Skylights have their own set of Energy Star criteria and are not addressed here.

An energy-efficient window has the following features:

• Durable, low-maintenance framing materials that reduce heat transfer and provide better insulation
• Two or more glass panes with a gas- or air-filled space; argon, krypton and other non-toxic gases insulate better than regular air
• Low-E coating that reflects infrared light for improved temperature control and also reflects ultraviolet light to protect interior furnishings from fading
• Spacers that keep glass panes the correct distance apart; non-metallic and metal/non-metal spacers also reduce heat transfer

Framing materials such as aluminum, composites, fiberglass, vinyl and wood are used in Energy Star qualified windows. Wood frames may be clad (covered) with aluminum or vinyl to reduce maintenance. Combination frames use different materials separately throughout to provide optimal performance (e.g. vinyl exterior and wood interior). Fiberglass and vinyl frames can be hollow or filled with foam insulation.

Some windows are better at keeping you warm, while others are better at keeping you cool. You should pick windows that are best suited for your climate. There are four Energy Star climate zones: Northern, North-Central, South-Central and Southern. You can identify your climate zone by using Energy Star’s Climate Zone Finder.

The Energy Star Qualification Criteria for windows based on Climate Zone is as follows:

• Northern:
  • U-Factor <= 0.30; Solar Heat Gain Coefficient (SHGC) any
  • U-Factor = 0.31; SHGC >= 0.35
  • U-Factor = 0.32; SHGC >= 0.40

• North-Central: U-Factor <= 0.32; SHGC <= 0.40
• South-Central: U-Factor <= 0.35; SHGC <= 0.30
• Southern:U-Factor <= 0.60; SHGC <= 0.27

Many online retailers sell Energy Star products. Make sure to check whether the windows you want to buy qualify for Energy Star in your climate zone. Be on the lookout for local rebates and promotions. You may also qualify for federal tax credits by installing Energy Star qualified products. Lastly, remember that you’ll enjoy long-term energy savings by replacing your windows with energy-efficient windows.