Choosing the Right Glass

U-Value, Visible Light and Solar Heat Gain – these important factors should be weighed when choosing windows for your home.

They all interact with one another to create a harmonious product that is right for you. The key to choosing the right glass package for your home is to find the right combination of performance values to suit your needs. Below are definitions of some of the key terms you need to know when researching and purchasing your new windows.

U-Value: A measure of the rate of non-solar heat loss or gain through a material or assembly. Tests are usually performed under conditions which simulate 0˚ outside and 70˚ inside with a 15 MPH wind. The lower a U-Value, the greater a window’s resistance to heat flow, and thus the better its insulating value.

Visible Light (VL): This is the fraction of the visible spectrum of light weighted by the sensitivity of your eyes that is transmitted through the window. Simply put, it represents the amount of daylight that the window lets in.

Solar Heat Gain Co-efficient (SHGC): The fraction of solar radiation admitted through a window including what is absorbed and subsequently released inward. The lower a window’s SHGC, the less solar heat it transmits and the greater its shading ability. Different climates require different SHGC values for maximum efficiency.


Low-E coating is a microscopically thin, virtually invisible, metallic layer deposited on the glass surface primarily to reduce the U-Value by suppressing radiant heat flow. Low-E coating is virtually transparent to the solar spectrum (visible light and shortwave infrared radiation) and reflective of long-wave infrared radiation.

Argon & Krypton are odorless, colorless, non-toxic inert gasses that can be used instead of air between panes of glass to increase insulation and energy efficiency. Argon is an excellent insulator, a good value and more readily available. Krypton is a denser gas and therefore a better insulator.

The performance of the spacer in the Insulated Glass (IG) unit is critical because it helps determine the energy efficiency of your window as well as its longevity. Since PPG introduced Intercept “Warm-Edge” Spacers in 1992, they’ve become, by far, the industry’s most trusted and proven spacer system. In fact, the Intercept Spacer System is now at work in more than 600 million windows in North America, a number that outpaces any other window spacer technology.


• Superior structural strength and durability

• Unique, one-piece U-Channel creates an effective thermal resistance to heat or cold migrating through the edge of the glass

• Allows for maintaining higher humidity levels in your home to retain heat better and increases the comfort level of your home

• Cost-effective and Energy Star compliant Window Performance Improvements*




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Certified Window Wholesalers Inc.


8647 Richmond Highway

Suite 247

Alexandria, VA 22309

Showroom located in Lorton Virginia



Montgomery County and Prince Georges County Office: 



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8647 Richmond Highway Suite 247 Alexandria, VA 22309 |  703-975-5500