With so many choices in replacement windows it can be hard to tell one window from another. How can a homeowner be sure he or she is getting a window that will deliver the promised energy performance? Just like you would do when shopping at the local supermarket, you should take the time to read the label.
The label, in this case, is the one attached to every quality replacement window by the National Fenestration Rating Council (NFRC). The 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.” The goal of the NRFC is to provide fair, accurate, and reliable energy performance ratings so that homeowners and others can compare different window products and make informed product choices.
The most important measure of a window’s performance is its U-Factor. The U-Factor indicates the rate of heat flow through a window. The lower the U-Factor, the more energy efficient the window will be. U-Factor measures the entire window unit — glass, frame, sash, spacers — and is the only measurement accepted by the U.S. Department of Energy’s Energy Star™ program. U-Factor ratings generally fall between 0.20 and 1.20. The lower the U-value, the greater a window’s resistance to heat flow and the better its insulating value.
Solar Heat Gain Coefficient
Solar Heat Gain Coefficient (SHGC) measures how well a product blocks heat caused by sunlight. The SHGC is the fraction of incident solar radiation admitted through a window (both directly transmitted and absorbed) and subsequently released inward. SHGC is expressed as a number between 0 and 1. The lower a window’s solar heat gain coefficient, the less solar heat it transmits in the house.
Visible Transmittance (VT) measures how much light comes through a product. The visible transmittance is an optical property that indicates the amount of visible light transmitted. VT is expressed as a number between 0 and 1. The higher the VT, the more light is transmitted.
Air Leakage (AL) is indicated by an air leakage rating expressed as the equivalent cubic feet of air passing through a square foot of window area (cfm/sq ft). Heat loss and gain occur by infiltration through cracks in the window assembly. The lower the AL, the less air will pass through cracks in the window assembly.
Condensation Resistance (CR) measures the ability of a product to resist the formation of condensation on the interior surface of that product. The higher the CR rating, the better that product is at resisting condensation formation. While this rating cannot predict condensation, it can provide a credible method of comparing the potential of various products for condensation formation. CR is expressed as a number between 0 and 100.
Be sure to look for the NFRC label on any window you purchase for your home? No label? Then you have no guarantee that the window will perform as it should.
To schedule a free in-home consultation with a representative from Rescom Exteriors, call us toll-free at (866) 410-5884. Or visit our web site at www.iwantnewwindows.com.