All About ENERGY STAR Ratings for Windows
ENERGY STAR qualified windows, doors, and skylights save you energy and money, increase the comfort of your home, and protect your valuable possessions from sun damage.
They are also better for the environment because when you lower your energy use, you lower the amount of air pollution generated by electric power plants.
NFRC is a non-profit organization that administers the only uniform, independent rating and labeling system for the energy performance of windows, doors, skylights, and attachment products.
Rating Window Efficiency Systems
When looking at different models of windows you should evaluate the manufacturer’s “U Value” and R Value” ratings.
The “U Value” is a measurement of heat conductance, and indicates a window’s tendency to transfer heat either in or out of your home.
The “R-Value” is a measurement of heat flow resistance. A window with a high R-value will lose less heat than a window with a lower R-value.
A window with a low U-value will lose less heat than one with a higher U-value.
NOTE: Most window manufacturers use R-values in rating their windows. Usually, window R-values range from 0.9 to 3.0, and U-values usually range from 1.1 to 0.3.
How to Compare Energy Efficiency Values for Different Windows
When comparing different windows, you should ensure that all U- or R-values listed by manufacturers:
- Are based on current standards.
- Are calculated for the entire window, including the frame, and not just for the center of the glass.
- Represent the same size and style of window.
Factors Affecting the R-Value of Windows
- The type of glazing material (e.g., glass, plastic, treated glass)
- The number of layers of glass
- The size of the air space between the layers of glass
- The thermal resistance of conductance of the frame and spacer materials
- The ”tightness” of the installation.
