Trying to decipher the numbers on a NFRC window label is an intimidating task for those that are not familiar with the industry. In order to choose the most efficient window for your home, a general understanding of window terminology is helpful.
There are three main sections to a window label: the qualifications, the “extras” and the performance ratings. One key indicator of an energy efficient window is the ENERGY STAR logo. The purpose of this logo is to distinguish the products that have met and/or exceeded the energy star standards. All energy star qualified products must meet strict energy performance criteria. It is always important to make sure the window you choose for your home has the energy star stamp of approval. This will lead to greater energy cost savings for your home. The label will also tell you how many states that this type of window is qualified for. Meaning what and how many types of climates the window is equipped for.
The National Fenestration Rating Council (NFRC) created and upholds a uniform national rating system for determining the energy performance of building elements. To openly communicate the rating of windows, they created the window label that houses the performance ratings for VT, SHGC, U-factor, AL and CR. The NFRC logo on the window label ensures that the window has been rated accurately. Testing on all products is done before determining the ratings of a window and only after the window has been certified, can a company display the NFRC logo on their product.
The next section of a window label is the “extras” section. This part of the label will house the retailer’s name, frame material, and list the additional enhancements to the window. This part will outline if the window is low-e, has insulation and what type, and any glazing that is applied to the window. Colder climates should always look for a window with a low-e coating. Low-e prevents cold air from entering your home and reduces the amount of cold air that is lost through the window. Glazing is another important element that high quality windows will have. Glazes will aid in keeping solar heat out of your home while also reducing the VT entering your home.
The performance ratings section is a little trickier to understand but aids in choosing the best window for the climate in your area. The goal of these specifications is to provide homeowners with the most energy efficient window for the climate in which they are located. To do this, you have to understand what the performance ratings mean and what range of numbers you should be looking for.
The U-factor measures the total heat flow through a window to the outside air. U-factors of 0.3 or less are ideal for all climates. A lower U-factor most benefits colder climates, however significantly benefits warmer climates when combined with a low SHGC. The lower the U-factor, the better the windows insulate.
SHGC stands for solar heat gain coefficient. This rating reports on the ratio of solar heat that passes through the glass. For climates that have very high temperatures, you want to look for a window that has a low SHGC, typically around 0.2.
Visual Transmittance, also know as VT, is the amount of visible light that enters your windows. VT is the factor that affects the amount of light that is let into your home. Every climate should look for a higher VT with a low-e coating.
Air leakage is air the escapes through small gaps in windows. Like VT, all climates should look for a lower value to prevent air from leaking out. The lower the AL, the less air escapes.
Condensation resistance helps prevent water from building up on your windows when the internal and external temperatures are opposite of each other. The higher the condensation resistance for a window, the less water build-up the window allows.