Understanding Energy Efficient Window Labels

Drafty, single-pane windows can be brutal on a home’s energy efficiency. In many older homes, window replacement is one of the most effective potential investments in long-term energy savings. But choosing from among dozens of window brands and models can feel overwhelming, especially if you don’t understand all the information on the window label.

Whether browsing for new windows online, in a catalog or in a retail store, the window label is the go-to source for data that makes it easy to compare window models. And once you know what each of the numbers on the label means, you’ll be able to make informed purchase decisions and get the most bang for your buck.

The Manufacturer’s Label

One panel of the label indicates the window’s manufacturer and usually includes a model number for the specific design. Listed below that are the basic product features, which may include:

  • Frame materials, such as wood, aluminum, vinyl, steel or fiberglass
  • Number of panes: single, double or triple
  • Type of gas filling the gap in multi-pane windows, usually argon or krypton
  • Glazing style
  • Low-E: a glass treatment that reduces harmful UV rays that can fade your furniture and carpets

The NFRC Label

You’ll also see four or five numbers on the label in large bold type. This data is calculated by the National Fenestration Rating Council, or NFRC. The NFRC is an independent organization that tests windows, doors and skylights in various performance criteria and certifies the results. The NFRC section of the label allows you to evaluate and compare key characteristics between window models:

  • U-Factor: a measurement of how effectively windows keep heat in your home. The lower the number, the more energy efficient the window during heating season.
  • Solar Heat Gain Coefficient: a measurement of how effectively windows block unwanted heat from outside. The lower the number, the more energy efficient the window during cooling season.
  • Visible Transmittance: a measurement of how much light a window lets in. Higher numbers mean more light, and potential savings on artificial lighting.
  • Air Leakage: a measurement of how much air a window lets in. The lower the number, the tighter the air seal. 
  • Condensation Rating: not every NFRC label will have this rating, which is a measurement of how well a window resists condensation. The higher the number, the higher the resistance.

The Energy Star Label

If a window meets certain performance guidelines for your geographical area, its label may also feature the Environmental Protection Agency’s Energy Star logo. This lets you see at a glance which windows have the most energy efficient properties. 

Because some windows are designed more for cold climates than hot climates and vice versa, there is no one-size-fits-all criteria to qualify for the Energy Star label. The criteria are divided into four U.S. regions: Northern, North-Central, South-Central and Southern. Energy Star only evaluates windows based on their NFRC measurements for U-Factor and Solar Heat Gain Coefficient.

To see the Energy Star criteria for your area, refer to Energy Star’s climate map for windows, skylights and doors.

Looking for other ways to make your home more comfortable while lowering your utility bills? Contact your local One Hour Heating & Air Conditioning to schedule an energy efficiency evaluation of your home and learn more about how much you can save.

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