ENERGY STAR ratings have been around for more than 20 years. The rating system started in the United States as a way to verify products that generally use 20 to 30 percent less energy than their counterparts, and it’s since been adopted by a range of other countries including Australia, Canada, New Zealand and Japan, as well as the European Union. Today consumers know to look for the ENERGY STAR logo when shopping for appliances, but not everyone knows they can purchase ENERGY STAR doors and windows. Installing ENERGY STAR windows is a good way to cut down cooling and heating costs in your home.
What Makes an ENERGY STAR Window?
There are three factors that determine whether a window is ENERGY STAR certifiable or not. They are the U-factor, the SHGC (solar heat gain coefficient), and the window’s air leakage. The U-factor indicates how easily heat flows through a window. The lower the U-factor, the more insulative the window will be. The SHGC, on the other hand, measures the amount of heat-causing light that can travel into a home through the window. Lower numbers here signify that less solar heat is allowed in. The air leakage rating (AL) measures the amount of air allowed through the frame and joints, per square foot of window space. Windows with a lower AL rating allow less air to flow through.
The type of windows you will need depends largely on what climate you live in. Because of this, the ENERGY STAR rating for windows varies by region. In northern climates a low U-factor and higher SGHC are necessary to receive an ENERGY STAR certificate. This allows your home to be properly insulated and take advantage of passive solar heat from the windows. In southern climates, the minimum U-factor rating for ENERGY STAR certification is slightly higher, but the SGHC is lower. This reduces the amount of excess solar heat in the home. That’s why it’s so important to buy the right ENERGY STAR windows for your location.
Window ENERGY STAR Requirements by Region
Here are the guidelines by region for ENERGY STAR to certify different windows.
- U-factor= .28 and SHGC = 0.32 or greater
- U-factor= .29 and SHGC = 0.37 or greater
- U-factor= .30 and SHGC = 0.42 or greater
North Central Guidelines
- U-factor= .30 or lower with
- SHGC = .40 or lower
- U-factor = .30 or lower with
- SHGC = .25 or lower
- U-factor = .40 or lower with
- SHGC = .25 or lower
ENERGY STAR Skylights
While all ENERGY STAR window requirements are stringent, the requirements for skylights aren’t quite as strict as they are for other windows. The U-factor can be considerably higher, and the SGHC doesn’t have to be as low in Southern locations. Even though the requirements are slightly more lenient, you should still pay attention to these ratings. Having a low U-factor skylight installed in a Northern home will allow a fair amount of heat to escape through the window.
Skylight ENERGY STAR Requirements by Region
- Northern – U-factor = .50 or lower with any SHGC
- North Central – U-factor = .53 or lower with an SHGC of .35 or lower
- South Central – U-factor = .53 or lower with an SHGC of .28 or lower
- Southern – U-factor = .60 or lower with an SHGC of .28 or lower
Air Leakage ENERGY STAR Requirements
In addition to meeting the regional energy efficiency requirements, windows must also be rated for air leakage in order to be ENERGY STAR certified. All windows, including skylights, must have an AL rating of less than 0.3 cubic feet of air for each square foot of window space.
Do a Bit More Research
ENERGY STAR ratings are a good place to start when shopping for windows, but just picking out a window because it is an ENERGY STAR window isn’t the best strategy. Some ENERGY STAR windows are much more efficient than others. Some are much more durable and some are worth the investment while others are not. Working with a window professional will help you choose quality windows that will be a good investment for the long term.