Windows. They come in all shapes, sizes, and materials. You have an endless amount of choices to make, but the one you could be peeling off is the most important. Yes, it’s those NFRC stickers that are placed on the glass with three numbers. These numbers tell you the energy performance and help with not only comparing the effectiveness of windows side-by-side but with figuring out which window is best for your climate.
Today, you will be introduced to the meaning of those numbers and their importance, so the next time you see one of these stickers while window shopping, doing construction, or in your household, you know what it all means.
What is an NFRC Label?
The National Federation Rating Council, or NFRC, is an independent council that tests, certifies, and labels objects like windows, doors, and skylights to help with making more informed purchase decisions.
The label is designed to create a standard metric for comparing window performance. There are four numbers you should see: U-factor, solar heat gain coefficient, visible transmittance, and air leakage. Because each number reveals a strength or weakness in the window glass, you can use the numbers to figure out if a window will work in your climate zone or not.
The reason the NFRC ratings are important is because it protects you, the consumer, from faulty merchandise. Windows are not a small expense, and no one wants to select a cheap window or one that is improper for their climate. With the NFRC rating, you know exactly what you are paying for.
Is it the same as Energy Star?
No, the NFRC and Energy Star ratings on your windows are different. Energy Star tells you when an appliance is energy-efficient. Meanwhile, the NFRC rating helps you compare such products with independent ratings of various values, so you can find the product that meets your needs the best.
The U-Factor
The first number you will see is the U-Factor. This number is a measurement of how well the window keeps heat from escaping the interior of a building. The lower the number, the better the window is at keeping heat inside. The range goes from 0.20 to 1.20, and the lower the number, the better the heat retention. If you live in a colder climate, seek out windows between the range of 0.20 and 0.39. Some superior quality windows, like a triple-gazed window, might be rated at 0.17.
Solar Heat Gain Coefficient
The second number across from the U-Factor is the Solar Heat Gain Coefficient (SHGC). The SHGC measures the window’s resistance against unwanted heat, which plays a role in how hot your living room becomes when the A/C goes off. From a technical standpoint, the solar heat gain coefficient takes how much solar radiation is let into the house versus how much is blocked out. The lower the SHGC, the less you spend on air conditioning. The range is anywhere from 0 to 1.
The lower the SHGC, the less solar heat you have in your household. In some states, like Maryland and Virginia, all Energy Star windows must have an SHGC of 0.40 or less.
But keep in mind that a low SHGC on every window might not be the best idea. Depending on the orientation of the window, such as west or south, in the sun or out of the sun, you can switch of the numbers a bit. For example, a window that receives full sun in the summer should have a low SHGC, while a window facing south in the winter can have a higher SHGC, helping you heat your home more efficiently.
If you live in the South, consider the 30/30 rule. U-factors under 0.30 should be paired with an SHGC of 0.30 or below, due to the hotter, more humid climate of the southern states.
Visible Transmittance
Next, there is Visible Transmittance (VT). This number describes how well a window can effectively light your home during daylight hours to help save you money on artificial lighting. The higher the number, the more natural light comes in. The range is between 0-1, and you want numbers closer to 1.
Visible transmittance are weighed against the other factors, so do not be surprised if more energy efficient windows have a lower VT score. For instance, a triple pane window has three panes of glass for light to pass through, meaning you get less light than a single pane. In other words, this makes a high VT and balanced U-factor and SHGC ratings a challenge to find. Base your decision on your priorities. Do you want natural light? Or do you want less heat loss/gain?
Air Leakage
Not all NFRC labels come with the air leakage number, and manufacturers often omit the AL because it’s not mandatory; but it is important to consider. Air leakage measures the amount of air that enters the room through the window. A low number means fewer drafts. The range is between 0.1-0.3.
Condensation Rating
Another optional rating for manufacturers is the Condensation Rating. You might not see it on many labels, but if you do, you should know that the higher the CR, the better the window will resist condensation.
Other Factors
The NFRC label is but one component in choosing an energy-efficient, durable window. Be sure to do your research on the various types of windows for you home, including the material type, insulation, and window films. By putting all these factors together, you can obtain windows that match your budget and serve your household year round.
Educating yourself on the determining factors put you ahead of the crowd. Knowing how to read an NFRC label on windows is the first step.
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