Vinyl Window Performance

Insulation

• Polyvinyl chloride is a plastic that's also a good insulator, according to the U.S. Department of Energy. The DOE indicates that vinyl window frames usually consist of PVC that contains ultraviolet stabilizers, which are substances that prevent sunlight from causing the PVC to break down. The insulating properties of a vinyl window frame increase significantly when its hollow interior is filled with insulation to reduce a home’s energy losses. The DOE considers insulated vinyl window frames to be superior to hollow vinyl frames.

Additives

• "Ask the Builder" columnist and builder Tim Carter asserts that every part of a vinyl window affects its performance, including the additives the vinyl contains. Carter recommends buying vinyl windows that have frames made with titanium dioxide. That chemical additive keeps vinyl from cracking and fading because it blocks ultraviolet light. In any case, it's important to take note of how a vinyl window is rated, because the quality of windows can vary widely.

NFRC Rating

• A rating system developed by the National Fenestration Rating Council simplifies the process for determining a vinyl window's efficiency. The NFRC uses a labeling system that shows each window's "U" value that applies to a window’s glass and frame. The lower the value, the more a vinyl window resists heat flow and insulates a home. Look for vinyl windows with a low "U" value if you're trying to reduce your home's energy losses. The “U” value generally ranges from 0.25 to 1.25.

Energy Star

• Another way to judge a vinyl window's performance is to look for an Energy Star label. The DOE and the U.S. Environmental Protection Agency developed the Energy Star program, which highlights and labels the most energy-efficient products. The "This Old House" home improvement website notes that windows meeting Energy Star requirements are as much as 40 percent more energy efficient than windows that meet standard building codes. The performance of all Energy Star windows is independently certified through testing procedures established by the NFRC.