A common goal for modern homeowners is making sure that their house is as energy efficient as possible, and one of the common ways of achieving this goal is installing energy efficient windows. However, because energy efficient windows can come with several labels, it can be hard to know if you are selecting the right option for your home.
Drafty, single-pane windows can be brutal on a home’s energy efficiency. In many older homes, window replacement is one of the most effective potential investments in long-term energy savings. But choosing from among dozens of window brands and models can feel overwhelming, especially if you don’t understand all the information on the window label.
Whether browsing for new windows online, in a catalog or in a retail store, the window label is the go-to source for data that makes it easy to compare window models. And once you know what each of the numbers on the label means, you will be able to make informed purchase decisions and get the most value for your money.
Certification labels are just as crucial as window ratings; you’ll run into these labels when window shopping, and it is a good idea to understand how they’re awarded.
- ENERGY STAR Certification Label: If a window meets certain performance guidelines for your geographical area, its label may also feature the Environmental Protection Agency’s Energy Star logo. This lets you see at a glance which windows have the most energy efficient properties. Because some windows are designed more for cold climates than hot climates and vice versa, there are no one-size-fits-all criteria to qualify for the Energy Star label. The criteria are divided into four U.S. regions: Northern, North-Central, South-Central and Southern. Energy Star only evaluates windows based on their NFRC measurements for U-Factor and Solar Heat Gain Coefficient.
- NFRC Certification Label: On your manufacturer’s label, you will usually see a number that is either four or five digits long. This number should be in bold and is used by the National Fenestration Rating Council (NFRC). An independent organization, the NFRC rates windows for their energy efficiency, and the number on the label can be used to choose the most efficient window model possible. The NFRC considers several factors when certifying a window model. Some of the information you can learn from the number on your label includes how much air leaks around the window, how effective the window is at keeping heat in your home, and how much light can get through the window.
- NAMI Structural Certification Label: The National Accreditation & Management Institute (NAMI) label certifies the window has passed all structural performance tests conforming to NFRC and AAMA standards, including forced-entry resistance, resistance to air infiltration, resistance to water infiltration and design pressure. It provides energy performance ratings based on values including U-Factor and SHGC. A NAMI Certification Label will indicate the standard to which the product was tested; the label should show the name of the manufacturing facility, the grade or performance level that was achieved, the series or model name of the product, and any other important information.
- American Architectural Manufacturers Association (AAMA) Certification Label: The AAMA Gold Label is sort of like a shortcut to identify high-performing, quality products. In order to be assigned this certification, a window must meet the American Architectural Manufacturers Association’s standards for air leakage, water penetration, wind and forced entry resistance, durability, and thermal window performance. Products have to be independently tested in an official AAMA laboratory, guaranteeing their reliable behavior in homes.
Not all manufacturers choose to test and certify their products with every organization, and most often opt for one certification over another. However, these four certifications serve as a great starting point during your window shopping.
The two labels you should make sure to find: the Energy Star label and the NFRC label. NFRC provides unbiased numbers for you to use in your decision making process, while Energy Star explains if those numbers meet their standards for superior performance. Keeping an eye out for these window performance ratings and certification labels can help you make the right decision for your home.
The following window ratings can be used to determine the efficiency of various windows—and help you sort through the plethora of options available:
When lower ratings mean better windows:
- U-Value/U-Factor: The U-Factor tells you how well a window insulates. This measurement tells us the rate at which the product conducts non-solar heat flow. U-Factor ratings tend to fall within a range between .20 and 1.20. The lower the U-Factor, the better insulation the window will provide, so when you’re shopping for energy-efficient windows, look for a product with a low U-Factor.
- SHGC: The Solar Heat Gain Coefficient measures how well a product can resist unwanted heat gain, which is especially important during summer cooling season. The lower the number, the less you will spend on cooling.
- Visible Transmittance: Visible transmittance, or VT, quantifies how much visible light a window allows into your home. The VT is expressed as a number between 0 and 1. There are a number of factors that can influence VT, including how many panes of glass a window has and any special coatings that may be on the glass, including a Low-E coating or a reflective coating on tinted glass. Windows use various degrees of tinting to control energy efficiency, solar heat gain and how much light can enter a space. A product with a higher VT rating will permit more natural light into a space, while you will notice more tinting on a product with a lower VT rating.
- Air Leakage: This measures the amount of air that a window allows to pass through. The lower the number, the more airtight the window. If you live somewhere windy, you might want a lower air leakage rating. Air leakage ratings typically range from 0.1 to 0.3.
When higher ratings mean better windows:
- DP: To start, let’s define what Design Pressure Rating means. According to AAMA (American Architectural Manufacturers Association), WDMA (Window and Door Manufacturers Association), and the NAFS (North American Fenestration Standard), a DP Rating is a rating that identifies the load – induced by wind and/or static snow – a product is rated to withstand in its end-use application. Basically, DP Rating measures the strength of a window. It will tell you how well your windows or doors will stand up to high winds or heavy snow. The higher the DP Rating the stronger the window or door.
- Condensation Resistance: The condensation resistance factor, or CR, measures the window’s ability to prevent condensation from forming and dripping down the glass panes. Condensation forms because of the temperature difference between the warm air inside and cold air outside coming in contact through the glass pane. The moisture in the inside air condenses on the glass and accumulates to drip down the pane and cause problems. The best rating is 100. CR is an optional rating and manufacturers may choose to not display it on their label.
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