U-Factors for Windows Explained

By December 6, 2013 window tips

Energy-Efficient WindowsChoosing an energy-efficient window is not as easy as one might think. There are many factors and ratings to consider. One of these factors is called the U-factor, which refers to the rate of heat loss. Find out more about this measurement and how it can affect your window shopping experience.

What is a U-Factor?

A U-factor is a rating given to energy-efficient windows. The National Fenestration Rating Council (NFRC) created this rating method to help consumers and inspectors determine the window’s insulation value. The Energy Star Program uses the window’s U-factor when evaluating it for certifications and rebate programs.

When it comes to U-factors, lower is better. Windows that are able to insulate a home better by resisting heat flow tend to have a lower U-factor, which is preferable. A U-factor of 0.30 is very good. This rating is typically given to double-paned windows. Some triple-paned windows have U-factors of 0.15, which is even better. The U-factor can apply to just the window glass or to the entire window. When the NFRC rates windows, it rates the entire window, including the spacers, glazing and frame.

Low U-factors are preferable in all types of climates, but even more so in hotter climates. However, cold climates can benefit from them as well, especially in the winter. There are recommendations for U-factors based on climate in the United States:

  • Cold climates in the North: Equal to or less than 0.30
  • Mixed climates in North and Midwest: Equal to or less than 0.32
  • Mixed climates in the central and South regions: Equal to or less than 0.35
  • Hot climates in the South: Equal to or less than 0.60

The U-Factor’s Relationship to R-Value

There are many ratings used to determine how good a window is at preventing heat loss, but many peopleconfuse U-factor with R-value because both are used to measure energy efficiency and insulation value. However, the main difference is that while the U-factor measures a window’s values, the R-value measures the insulation in other areas of the home, such as the roof, under the floor and behind walls.

U-factor and R-value are also related in terms of mathematical equations. If you know a window’s U-factor, you can figure out its R-value; just turn it into a fraction by dividing 1 by the U-factor. If the window, for example, has a U-factor of .25, the R-value would then be 4.

Get the Best Windows for Your Home

If you’re ready to upgrade your windows, let Window Choice help. There are many types of energy-efficient windows available, and some insulate better than others. Our helpful and informative staff can help you choose the right windows for your needs. We have spent more than a decade helping Ontario residents save money on their energy bills. Contact us at (905) 461-2267 or (866) 230-5115 for a quote.

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