ENERGY STAR PARTICIPANT

We spend millions of dollars every year to heat our homes and businesses. That is why it is so important to understand the role that windows and doors play in how buildings use energy. With heating and cooling costs a big concern among homeowners, consider the thermal dynamics of the windows you choose. Look for the Energy Star label, which indicates compliance with government mandates for energy conservation.

Many consumers are aware of R-Values – a measurement of a product’s resistance to heat loss – and have learned that materials with higher R-Values are more energy efficient. R-values are still widely used within the industry, however, windows are very different from other building products in that they operate, allow light in and allow people to see out. They react to outside air temperatures, sunlight and wind, as well as indoor air temperatures and occupant use. They interact with their environment in ways that insulation does not. Windows are strongly affected by solar radiation and airflow around them yet the R-Value does not accurately reflect this interaction.

Another way (and one of the best ways) in which the energy efficiency of window products can be determined is in terms of thermal transmission, or the U-Factor. U-Factor measures how well a product prevents heat from escaping a building and is particularly important in winter months. U-Factor ratings generally fall between .20 and 1.20. Emissivity is the ability of a product to absorb certain types of energy and radiate that energy through itself and out of a room. The lower the conductivity and emissivity of the glass, the lower that rate of heat loss, thus the lower the U-Factor.

The biggest difference between the U-Factor and R-Value is that the U-Factor measures the rate of heat transfer through window materials, taking into consideration the airflow around the window and the emissivity of the glass, while the R-Value measures conductivity and the resistance to heat loss. Where R-Values rate the energy efficiency of a single component (i.e. the sealed glass unit of a window), U-Factors rate the energy efficiency of the combined materials (i.e. the sealed glass unit, frame material, weather stripping etc.). Because each of these components works together as a unit, the U-Factor is used to indicate the energy efficiency of the entire assembly.