Energy Efficient Window's Labels and Ratings: What do they mean?

Written by AnonymousApril 21, 2011
Energy Efficient Window's Labels and Ratings

Discussing What Labels and Ratings for Energy Efficient Windows Mean

As your living situation changes, the reasons to replace your windows will change. You may decide that your home needs more light as it ages or a room in the home may become too stuffy, requiring more ventilation. Light and ventilation are only two reasons homeowners replace windows. The main reason for window replacement is energy loss. In newer and older homes, worn or standard windows may have to be replaced to help reduce energy loss.

Installing modern window styles with advanced energy efficiency technology is the solution homeowners choose most often. But how can you tell if a window is truly energy efficient? All you have to do is check window products for the National Fenestration Rating Council (NFRC) label. The label lists information about the energy performance of windows including ratings for air leakage, solar heat gain, and condensation resistance.

Energy Performance Ratings

The NFRC’s goal is to list five ratings per label. These ratings determine whole product performance. The ratings are determined for a fixed set of environmental conditions and a specific product size. The ratings are:

  • U-Factor is important during the winter season. It determines how well a window prevents heat loss. Ratings range from 0.20 and 1.20. The lower the rating, the better the window is at keeping heat in.
  • Solar Heat Gain Coefficient (SHGC) measures how efficient a window is at blocking heat from the sun. Ratings are between 0 and 1. The lower the rating, the better the product is at blocking unwanted heat gain.
  • Visible Transmittance (VT) measures how much light passes through a window. Ratings are between 0 and 1. If the rating is high, more light is allowed to pass through for maximum visual comfort and reduced energy use.
  • Air Leakage (AL) measures how much outside air a window will allow in. Ratings fall between 0.1 and 0.3. Lower ratings mean the product is better at keeping air out.
  • Condensation Resistance (CR) measures how well a product resists condensation. Ratings fall between 1 and 100. The higher the number, the better the window is at resisting condensation.

Although the NFRC does it’s best to list all five ratings, some labels may not include everything. The manufacturer has the option to exclude air leakage or condensation resistance. Missing information may be an indication that the window does not perform as well as windows with all five ratings. 


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