What Exactly Does an Energy Efficient Window Do

The continuing depletion of the earth’s energy sources has raised everyone’s consciousness to a level where more people worldwide are now paying attention to the importance of green living. Homeowners all over the country are finally pro-actively “doing their part” to preserve the environment—and they’re starting with their own homes.


Many are opting to have their windows changed, for one thing. The windows available on the market today are no longer limited to the old models that often used to let drafts in or allowed the sun’s damaging rays to enter a home unfiltered. New window innovations continue to improve on energy performance, and regulatory (albeit voluntary) organizations now oversee these products. Some of these include:Energy-Efficient-Window-1

  • ENERGY STAR. Created by the Environmental Protection Agency, ENERGY STAR is a voluntary program that labels energy efficient products, homes, and businesses. When you choose energy efficient windows, make sure they’re labeled ENERGY STAR.
  • National Fenestration Rating Council. The NFRC is a non-profit organization that conducts independent testing and rating of fenestration products, including windows. The NFRC findings are the basis upon which ENERGY STAR awards labels.

The truth is, most consumers, while they DO care for environment, don’t really understand exactly what the windows are being labelled and tested for. Many still ask the question: What exactly am I getting when I buy energy efficient windows? Here are some things you’d probably be interested to know:

Heat control. Heat transfers through windows by way of conduction, convection, and radiation. Energy efficient windows are designed to limit the potential of unwanted heat gain or loss, which can be measured through these two values:

  • U-factor. U-factor is the measure of heat loss through the window; the lower the number, the better the window’s insulating properties. Low U-factors are ideal for warm climates.
  • Solar heat gain coefficient (SHGC). SHGC measures the heat admitted and radiated into the interior of the home, expressed in values between 0 and 1. Lower SHGCs mean lower amounts of transmitted heat.

Daylighting. One of the main purposes of windows is to provide daylight, which reduces the need to use mechanical systems. Visible transmittance (VT) measures the amount of visible light that passes through the windows. High VTs mean more daylight.Energy-Efficient-Window-2

Ventilation. Ventilation, too, is a primary function of windows – but, with older windows, the home’s ventilation requirements can very easily turn into a liability, as air leakage is common. Air leakage (AL) measures the cubic feet of air that leaks through the window; lower ALs mean less air leaking.

Condensation resistance. How well a window unit resists the formation of condensation is expressed through condensation resistance or CR. Higher CRs equal higher resistance. When shopping for energy efficient windows, you may come across products that do not have this rating, as it is optional.

An energy efficient window system is not just about choosing the right glazing or framing material, however. You can improve your windows’ thermal performance by considering these tips:

  • Install window treatments. Drapes, shutters, awnings, and other window treatments can help reduce glare on hot summer days, as well as keep the rain out when the weather turns sour. In addition, they can supplement the protection of your interior decorations and furniture.
  • Choose the right contractor. Energy efficient windows perform best when properly installed, and a good contractor can make a big difference towards ensuring that you are able to maximize your savings and benefits. In addition, state and local building codes have to be followed during the process – something that a licensed window contractor knows is of utmost importance.Energy-Efficient-Window-3

Author Bio

Sam Heer is President and owner of Renewal by Andersen of Central Illinois. Over the past 18 years, he’s worked closely with well-known retailers and industrial suppliers, among them Home Depot, Ace Hardware, Sears, and Grainger. He initially joined the Renewal by Andersen team as General Manager in 2003, then moved on to become VP of Sales at Prairie Home Alliance (one of the largest home improvement contractors in the state of Illinois) from 2009-2013. A well-respected civic and community leader, Sam is trustee and Board member of several notable organizations in Morton, Illinois. Read more of his blogs on the company’s website.


More Reading

Post navigation


Leave a Reply

Your email address will not be published. Required fields are marked *