The performance of your home is heavily dependent on every component functioning as it should. One area of the home that is often misunderstood is the windows. These windows are an important part of the home’s functionality and aesthetics, responsible for energy efficiency, protection against the elements, and ventilation—as well as design and curb appeal.

Because the windows of a home are so critical to its performance and appearance, it’s important to understand how to properly evaluate replacement window options before settling on a product and scheduling a window installation. While qualified window contractors can give advice on what’s best for the home, those interested in using their own judgment when purchasing new windows should learn more about how they’re rated.

Nearly all windows have stickers on the window glass itself that help consumers determine the performance of the replacement windows they’re interested in. In this guide to window ratings from Southwest Exteriors, we’ll explain what that information means and how you can interpret window ratings to find the best performing products for your investment.

Reading the Sticker 

For the unprepared, the information contained on these stickers can be hard to interpret. Fortunately, each section is easily broken down into the following sections:

  • U-factor and R-Value: These two factors both have to do with how well the window manages heat. The U-factor, also known as U-value measures the degree of heat transfer, which is heat gain or loss through the glass. On the other hand, R-value is a measure of heat resistance. As a rule, you want windows with a low U-factor and a high R-value.

  • Solar Heat Gain Coefficient (SHGC): This measure tells us how much solar radiation is admitted through the window. This includes direct transmission and the amount of radiation absorbed and then released inward. The score ranges from 0 to 1. The closer to zero the score is, the better the window is at minimizing solar heat transfer.

  • Visible Transmittance: Windows are designed to let in light. As such, a window’s ability to let in visible light is scored with visible transmittance. A higher score indicates that more visible light passes through then window during the day.

  • Air Leakage: Even the best windows can be subject to air leakage. With air leakage, heat loss or gain can occur through cracks in the window assembly. The scale ranges from 0.1-0.3 with 0.1 being the desired score.

  • Sound Transmission: High-quality windows should block out most of the neighborhood noise. With high-performance windows, sound transmission is reduced. Look for an STC value of 26-32 for normal windows and a value of 48-54 for soundproof windows.

  • Condensation Resistance: Proper window performance means that condensation is resisted to an extent. This is measured with the condensation resistance factor. The score ranges from 30-80 with 80 being the best score possible.
  • Design Pressure: This metric measures how much of a load the window can withstand. This load comes from wind or static snow. The better the design pressure rating, the more pounds per square foot of pressure the window can withstand. The DP score can range from 15-50. If you live in a high wind area, we recommend looking for a window that scores at least a 30 in this category.

Interpreting Organizations and Programs

The ratings for windows aren’t arbitrary calculations. Like anything that has a rating system, there’s a governing body that oversees that category. Some of the most common ones include:

  • The R5 Volume Purchase Program: This was a purchase program designed to push for better energy-efficiency at a cheaper rate. Windows in this category boast an R-value of 5 or U-factor around 0.2. Usually, these windows are triple-pane windows. While the energy efficiency cannot be ignored, the truth is the average cost has not seen any significant reduction.
  • National Fenestration Rating Council: This the council is responsible for the development of a window energy rating system for the window as a whole. The council is an independent body and focuses on doors, skylights, and windows. The categories under this council include U-factor, solar heat gain coefficient, visible transmittance, and air leakage.

  • Energy Star: This governing body strictly focuses on the energy efficiency present with each window. If the window boasts an Energy Star designation, it has met certain energy performance metrics to be deemed as highly energy-efficient.
  • AAMA Certification: This is a certification applied to windows that pass stringent testing for each component of the finished window. Everything from the latch to the glass itself is tested. Windows that boast this certification are considered to meet the best-quality assurance standards.

San Antonio’s Top Choice for High-Quality Home Remodeling Services

At Southwest Exteriors, we focus on delivering the absolute best products at the most affordable rates on the market. Combined with our commitment to personalized customer service and expert installation procedures, our customers enjoy a truly stress-free experience when replacing their home’s windows.

Whether you’re ready for new replacement windows, a brand-new roof, a beautiful new entry door or replacement siding—our team at Southwest Exteriors is here for you. Give us a call to speak with one of our agents about your exterior remodeling ideas, including installation services and more. Or, fill out our online form to schedule a free, in-home pricing estimate and design consultation.