How Long Are Windows Efficient?

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When it comes to your windows, energy efficiency is key. A leaky fenestration can cost you a fortune in energy bills, so it’s important to keep an eye on yours.

Look for NFRC ratings to gauge your window’s performance. Select a high visible transmittance and low condensation resistance to allow in plenty of natural light, while keeping your home comfortable. Choose a low U-factor to reduce heat loss in cold climates.



ENERGY STAR is a government program that promotes energy efficiency. It verifies that a product meets strict standards set by the Environmental Protection Agency. It can be used in homes, buildings and businesses.

The ENERGY STAR logo is seen on products window company, appliances and other equipment that meet certain energy performance criteria. These include energy-efficient lighting, low standby power, and other features. ENERGY STAR products and buildings save money, improve comfort, and reduce pollution.

The ENERGY STAR label is easy to recognize, with a blue symbol that shows a stylized word “energy” and a star. It is a government-backed standard that makes it simple for consumers to choose energy-efficient products, homes and businesses. Commercial building owners can use ENERGY STAR Portfolio Manager to benchmark their energy usage and receive an ENERGY STAR rating, similar to the home ratings. These ratings are based on a comparison of building data with a national average. A 1-100 rating is determined based on a building’s overall energy consumption and a series of metrics, including utility bills, operating hours, carbon dioxide emissions, indoor air quality, and water use.


Low-E windows have glass that is coated in invisible layers of metallic oxide. The coating allows natural light to enter your home while deflecting UV rays and infrared heat back out into the environment where it belongs. This helps to improve the window’s insulating properties and reduces electric space-cooling requirements in warm climates.

The metallic oxide coating also helps to extend the life of your furniture, carpets and curtains by blocking damaging UV rays. These rays are the main cause of upholstery fade and fabric wear over time.

There are two different types of low-E coatings: passive and solar control. Passive low-E is applied to one of the four surfaces in a double pane insulated glass unit (IG) while solar control low-E is added to the surface that faces the sun. Generally, solar control low-E glass is best in cold climates where the SHGC value is lower and less solar heat can penetrate the glass.


In northern climates, where heating is a major expense, windows with a low U-factor are more important than in other areas. The lower the U-factor, the better a window will insulate.

Typically, windows with a lower U-factor will have a lower Solar Heat Gain Coefficient (SHGC), too. A low SHGC means the window allows less sunlight into your home while still allowing in natural light.

While a low U-factor is important, it’s not the only factor to consider when choosing energy efficient windows. Another important factor is the R-value. R-values describe how well other components in your home insulate, and should be taken into account when selecting a window.

To make a wise purchase, look for windows with a lower U-factor and an R-value that meets or exceeds your needs. An experienced professional can help you determine what type of windows are right for your home. The National Fenestration Rating Council, or NFRC, tests and certifies energy-efficient products like windows.