How to Interpret Window Ratings

Purchasing windows for your home can help upgrade the appearance and style of your home, provide better energy-efficiency, and help replace damaged, worn-out materials with newer and more effective ones. However, finding the best products for your home window installation means reading the labels—a task that can prove quite overwhelming if you aren’t sure what all of the different ratings mean.  

Miracle Windows and Sunrooms is one of Florida’s most trusted window contractors with over 100 years of combined experience in the industry. While we’re quite used to evaluating the energy performance label designed by the National Fenestration Rating Council, we know how confusing it can be for our customers. In this guide, our experts at Miracle Windows and Sunrooms will explain what these ratings mean and why this critical information is important for you when shopping for your next replacement windows.

U-Factor vs R-Value

There are many ways to rate windows and how they resist and transfer heat is one of the most sought after ratings. These ratings are measured by a U-Factor, the measure of heat transfer, and R-Value, the measure of heat resistance.U-Factor ratings for windows are typically between 0.20 and 1.20. Lower U-Factors offer better resistance to heat flow, so the better the window’s insulation performance will be.

Solar Heat Gain Coefficient

To measure a window’s solar heat that it transmits, you will need to find out what the solar heat gain coefficient is. The SHGC is a measurement of the fraction of solar radiation that makes it through the window. It can be transmitted directly or absorbed and then released as heat into the home. The ratings fall between 0 and 1, and like the U-Factor rating, the lower the number, the higher the performance. In Florida (and in other hotter climates), choose windows with an SHGC rating of .40 or lower for more protection against the solar heat.

Visible Transmittance

When it comes to finding out how much light you want to let in your home through the windows, you will need to look at the Visible Transmittance. Otherwise known as VT, the visible transmittance refers to a measurement of the amount of light in the visible portion of the spectrum that passes through your window.

Air Infiltration

Just as it sounds, air infiltration refers to the rating of a window’s ability to allow air to enter the room. This is going to be measured in cubic feet depending on the specific time frame that is allotted for the measurement. You will want to aim for a rating between 0.1-0.3 for the best performance.

Water Penetration

A water penetration test is going to measure how much water will be allowed to pass through a window when applied to the face of the window. These tests are performed at 15% of the Design Pressure, in most cases.

Sound Transmittance

Sound transmittance is a measurement of a window’s ability to reduce sound. You are going to want to look for windows with higher STC ratings as they will provide the best sound reduction performance.

Condensation Resistance Rating

The condensation resistance rating of a window measures condensation. In other words, the rating shows us how well the window can resist the formation of condensation on the inner surface of the window. Windows with higher condensation resistance ratings will resist condensation better than those with lower scores.

NFRC Rating

The NFRC, or Nation Fenestration Rating Council, provides consumers with energy performance ratings for windows, doors, and skylights. These ratings will determine how energy efficient a window is.

AAMA Certification

AAMA certification refers to products that are resistant to air leakage, water penetration, and wind pressure. The American Architectural Manufacturers Association gives this certification to products that meet all of their requirements, and is a great certification to look for when shopping for windows.

Window Contractors in Jacksonville

Serving the greater Jacksonville area since 2006, Miracle Windows and Sunrooms has provided Florida homeowners with the highest quality products and industry-leading customer services. Whether you need new windows, doors, or a beautiful new sunroom installation, our team of expert window contractors can build the comfortable, gorgeous home you’ve always wanted—at a price you’ll love.  

If you’d like more information about our replacement windows, or other products and services at Miracle Windows and Sunrooms, don’t hesitate to give us a call to speak with an agent now. Or, to request a free, in-home estimate and consultation for your window installation, just fill out the online form.