The National Fenestration Rating Council (NFRC) is an organization that compares different window, door and skylight products, and rates these products’ energy efficiency characteristics. Their ratings are then placed on the product so consumers are aware of how the product performs in terms of energy conservation.
The problem is, some of the terms on the labels are somewhat technical in nature, so you might find it difficult to understand what the ratings mean. In this post, we give you a brief overview to help you understand them.
An NFRC Energy Rating label consists of four main quadrants:
- Solar Heat Gain Coefficient
- Visible Transmittance
- Air Leakage
Here’s a brief explanation of each quadrant and what figures you should be looking for.
- U-Factor – U-Factor is a unit of measurement that indicates the amount of heat loss. It measures the amount of heat inside the home that can escape through the window’s glass panels and frame. The lower the U-Factor rating, the better the window’s insulation properties, which would mean that your home will need less energy to keep it warm inside. Most windows with double glass panes have a U-Factor rating of 0.30, which is far better than ordinary, non-energy efficient windows.
- Solar Heat Gain Coefficient (SHGC) – This unit of measurement indicates how much solar heat passes through the window’s glass panels and frame. Windows with a low SHGC rating prevents more solar heat from entering the home through the window, which translates into lower energy costs to cool the home. The SHGC rating is a figure between 0 and 1. Look for windows that have an SHGC rating closer to 0.
- Visible Transmittance (VT) – Although you’ll need to prevent heat from passing through the window to conserve energy, you also want as much light as possible to pass through as well. If more natural light enters the home, you’ll consume less energy in lighting costs. The amount of natural light that passes through a window is measured in visible transmittance. This rating is between 0 and 1. You’ll need to look for a rating closer to 1, which would mean that more natural light is getting through the window.
- Air Leakage (AL) – Heat can also be lost through air passing through small gaps in the window’s structure. The fewer gaps there are in the structure, the less air leaks, which would mean lower energy consumption to keep the room warm. Look for the lowest air leakage rating.
In the next post, we’ll take a look at the importance of selecting good window frame material. Stay tuned!