What Makes An Energy-Efficiency Window?

2 Key Questions To Ask

Have you ever walked past a window in the middle of summer and noticed an instant temperature change? 

It’s almost as if the window glass amplifies the streaming sunlight, making it feel even hotter than outside. 

Maybe you’ve noticed your AC unit seems to be working harder and harder over the years. Or perhaps you’ve noticed your energy bills increase during the extreme seasons.

Could your windows be getting old? Could it be that your house was built with low-quality windows?

No matter the circumstances, you know you want to replace your windows with something energy-efficient that will help regulate the internal temperature of your home.

If you’re in the market for top-tier, energy-efficient windows, you need to understand how to read window energy ratings and know how they affect your home. 

Lucky for you, we’re here to help. 

As a San Antonio window replacement company since 1989, Southwest Exteriors has helped hundreds of homeowners make their homes more energy efficient with high-quality replacement windows. 

Education is important to us. We want you to have all the information you need to find the right replacement windows that will meet all your needs. 

So, we want you to understand what measurements are used to determine the energy efficiency of a window so you can find the best window and contractor for your home. 

This article will outline two questions to look at to determine the energy efficiency of a window. We will then define energy ratings in these categories that measure the energy efficiency of a replacement window. 

After reading, you’ll be able to understand window energy ratings and decipher the energy efficiency of a window. Then, you can find the right replacement windows that will meet your needs for improving the energy efficiency of your home. 

2 questions to consider to find an energy-efficient window 

When you think about the energy efficiency of a window, it can seem like an overwhelming topic. 

You may know a broad definition of what energy efficiency is. But, what specifically defines how energy efficient a replacement window is? 

To determine how energy efficient a window is, you will want to look at three questions pertaining to how the window performs. They are: 

1. How well does the window block heat?
2. How well does the window insulate your home?

How do you answer these questions, you may ask? 

Each can be measured by using various energy ratings set forth by the National Fenestration Rating Council (NFRC) and ENERGY STAR, which is backed by the U.S. Environmental Protection Agency (EPA). 

Here we will dissect these two questions and what energy ratings are used to measure the energy efficiency of a replacement window. 

Then, you will know what energy ratings make up the energy efficiency of a window, how to tell if a window is energy efficient or not, and how the ratings affect your home. 

1. How well does the window block heat?

The biggest indicator that a window is energy efficient is if it blocks solar heat and harmful UV and infrared rays. 

When sun heat and solar rays are able to penetrate through a window, it heats up the interior of your home and can damage what’s inside. 

To know how well a window can do this, you will want to look at three energy rating measurements: the solar heat gain coefficient, the UV percentage, and the infrared percentage.

• Solar Heat Gain Coefficient (SHGC)

This measures the amount of solar heat that comes through a window, ranging from 0 – 1. The U.S. Department of Energy’s consumer resource, Energy Saver, says the lower the SGHC, the less heat from the sun comes through a window. 

The lower the number, the better the window blocks solar heat. 

• UV Percentage

This measures the percentage of UV rays that penetrate through the window. The lower the UV percentage, the fewer UV rays come through your window. 

So, a window with a low UV percentage will block more UV rays. 

• Infrared Percentage

This is the percentage of infrared rays that penetrate through a window. These light rays are invisible to the eye but produce heat just like any other ray on the electromagnetic spectrum. 

Similar to UV percentage, the lower the infrared percentage, the fewer infrared rays penetrate through the window. 

How do these ratings affect the energy efficiency of a window?

These energy ratings all have to do with heat and how well a window blocks solar heat, UV rays, and infrared rays. 

When analyzing these ratings, you want to look for low numbers. The lower the number of the rating on the window, the less heat and rays penetrate through the window. 

This means that your home is not only staying cooler during the summer, but you, your furniture, and the interior of your home is protected against harmful rays that are damaging.  

2. How well does the window insulate your home?

After looking at how well a window blocks heat and solar rays from your home, the second largest indicator of an energy-efficient window is one that is a strong insulator. 

A window covers a large opening in the frame of your home. If that opening is not sealed tightly with a high-quality window, then your home is susceptible to air escaping and passing in and out of your home. 

How well a window can insulate tells you how well that window will protect, maintain, and improve the regulation of the internal temperature of your home. 

To measure how well a window can insulate, there are two ratings to look at: the air infiltration rating and the U-factor. 

• Air Infiltration Rating

This rating measures “how many cubic feet of air passes through a window per minute in relation to the size of the window,” according to a blog post by window manufacturer Marvin. 

This rating is measured from 0.0 - 0.3 (cfm)/ft2, which is the rate at which air passes through the window. 

The lower the air leakage rating, the less air passes through the window. 

• U-Factor

This measures how well a window can insulate. According to the U.S. Department of Energy, the U-Factor for windows generally ranges from 0.20 – 1.20.

With this measure, the lower the number, the better insulator it is. 

How do these ratings affect the energy efficiency of a window?

The air infiltration rating and U-factor of a window will tell you how well the window keeps your home insulated. 

The better a window can insulate, the more energy efficient it makes your home. This helps your home stay cool during the summer and warm during the winter. 

If a window is not a good insulator, it is not protecting your home. So, if you want an energy-efficient window that will keep your home insulated, look for a low air infiltration rating and low U-factor. 

Finding the right energy-efficient window for your home

Now you know the two crucial questions to consider to find energy-efficient replacement windows for you. 

The two biggest indicators that a window is energy efficient are if it blocks heat and harmful rays and insulates your home. 

To measure these energy ratings, you want to look at the solar heat gain coefficient, UV percentage, infrared percentage, air infiltration rating, and U-factor. 

By understanding these ratings and how they affect your home, you will be able to find the right window and the right contractor to work with that offers replacement windows that meet your energy efficiency needs.

At Southwest Exteriors, we offer the most energy-efficient replacement windows for San Antonio homeowners. 

But, even if you don’t work with us, we want you to get the best windows that will meet all your needs for energy efficiency. 

Educating and informing you on how to understand what makes a replacement window energy efficient is our first priority so you can find the perfect window for you. 

A large part of understanding the energy efficiency of a window is learning about different window glass types.

This article will outline six different types of window glass, like Low-E, gas-filled, tinted, and more. Then, you’ll be able to choose the right glass for your replacement windows that won’t only look how you want but perform and meet your energy efficiency goals.