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WINDOWS: U-Factor, Solar Heat Gain Coefficient…what does it all mean?!

June 13, 2008

nfrc window fenestration ratingIt is time to make THE window decision for your remodel.  If you are looking for energy efficient windows then you will run into many new vocabulary terms:  U-Factor, SHGC, Visible Transmission…   And all you want are windows that will save energy, and look amazing when your remodel is done! 

So what do all these new vocabulary words mean? Turns out this new language does not find its root in Latin.  These terms actually belong to the National Fenestration Rating Council (NFRC).  Fenestration, when it comes to your home, are windows, doors, and skylights.  The NFRC is a non-profit that develops and publishes standards for fenestration performance.  Windows, doors and skylights are then labeled with a sticker like the one example in the upper right.

Turns out that understanding the terms and acronyms on this label can help you quickly navigate the glassy waters as you are considering one window over another – assuming you are looking for efficient windows that transmit a great deal of light into your home!   Here is your guide for the label, consider yourself now dangerous:

  • U-Factor:  Measures how well a window, door, or skylight prevents heat from escaping.  Ratings usually range from 0.20 to 1.20.  The lower the number, the more efficient your fenestration product.  U-Factor will change as window sizes change.
  • Solar Heat Gain (SHGC): Measures how well your new window blocks heat from sunlight – keeping your home cooler.  The lower the SHGC, the lower the heat gain through a window.  SHGC ranges from 0 to 1.  SHGC will change as window sizes change.
  • Visible Transmittance (VT):  Measures the amount of visible light transmitted through your new remodel window.  This will determine the amount of daylighting you will receive, ultimately reducing your need for lights.  VT is measured between 0 and 1.  The higher the value the more light.
  • Air Leakage:  Measures the amount of air that could pass through your window (yes, even when it’s closed).  The lower the AL, the less air will pass through cracks in the window assembly.
  • Condensation Resistance:  Measure the products ability to resist moisture on the interior surface of the window.  The higher the rating number, the more resistant your new window will be to condensation forming.  CR is expressed as a number between 0 and 100.

So as you are browsing your Pella dealer, Andersen showroom, The Home Depot, or Lowe’s you now have one more way to compare your window, door or skylight purchase - efficiency.

 

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