The traditional windows used in the United States are a double hung, single glass pane set in a wooden frame. Unfortunately, these windows are poor at keeping out cold and excess heat. ENERGY STAR certified windows better insulate the home and help filter out harmful ultraviolet light improving indoor comfort. They also save you money on heating and cooling costs.
If you have these traditional pane windows, chances are you are spending hundreds of extra dollars a year in heating and cooling expenses than you would if you had ENERGY STAR certified windows. In this article, we take a look at how replacement windows are rated for energy efficiency.
ENERGY STAR is a program jointly run by the Environmental Protection Agency (EPA) and the Department of Energy (DOE). The program aims to help consumers, businesses, and industries save money and protect the environment by buying and using energy-efficient products and practices. Submitted products are tested, certified, and then labeled based on their energy performance ratings. For example, ENERGY STAR certification for windows is based on solar heat gain coefficient ratings and U-factor based on the National Fenestration Rating Council (NFRC) standards. This council gives consumers energy performance ratings and other helpful information about windows, doors, and skylights.
Energy Efficiency Ratings for Windows
Heat Gain and Loss
Windows can gain heat through direct conduction, thermal radiation, solar radiation, and air leakage through and around them. These are measured according to the following energy performance characteristics.
U-factor. It’s the rate at which the window transmits non-solar heat flow. The U-factor may refer to just the glass or glazing alone, while the NFRC U-factor represents the whole window performance, including space materials and frame. The lower the U-factor, the more energy-efficient the window.
Solar Heat Gain Coefficient (SHGC). It is the fraction of solar radiation admitted through the window. The lower the score, the less the solar heat it transmits and the better the shading ability. Windows with high SHGC are more effective at collecting solar heat during the winter. The one with low SHGC is more effective at reducing the cooling loads during the summer by blocking heat gain from the sun.
Air Leakage. It’s the rate of air movement around the window under specific pressure differences. A window with a lower air leakage rating is tightly sealed and much better for energy efficiency.
Visible Transmittance (VT). It is a fraction of the visible spectrum of light transmitted through the window’s glazing. A window with higher VT transmits more visible light. The VT is a number, and the VT you need for a window is determined by the home’s daylight requirements and whether you need to reduce the interior glare.
Light-to-Solar Gain (LSG). It’s the ratio between the VT and the SHGC. It gauges the relative efficiency of specific glass or glazing in transmitting daylight while at the same time blocking heat gain. The higher this number, the more the light transmitted without adding excess heat.
Windows By Toll
When selecting windows, consider the house’s orientation, natural light requirements, and climate environment. For example, extreme heat or cold will require a different window than a home in a temperate climate. Windows By Toll can help. Our experts will recommend windows that will meet your energy and budget needs. Contact us today at 203-580-9945.