All the parts of a good window are manufactured to form a unit that is energy efficient and prevents heat loss. The frame is the material that holds it all together and if installed correctly you could save on utility bills in the winter by preventing heat loss from inside and in the summer by preventing heat that will transfer into the home. Heat will travel from hot to cold objects.
For the purposes of this discussion the frame is actually made of the sash and frame, which together comprise 10-30% of the total window area. The sash is the moveable section that contains the pane or panes of glass. As in the sliding sections of a double-hung window, one sash is in front of the other and locks into place for security. The sash on a double-hung window may also tilt in for easy cleaning. The frame and sash are typically made of the same material so we will refer to them together as the frame.
There are a few different materials to construct the frame. The material will determine its strength, lasting beauty, and thermal dynamics. The four most popular materials for home replacement windows are aluminum, wood, vinyl and fiberglass. Steel is usually reserved for commercial buildings.
Thermal performance for an aluminum frame is poor, at best. Aluminum is a good conductor of heat. Wood performs better in preventing heat loss. However, wood is less durable but can be wrapped on the exterior with vinyl or aluminum to help preserve the wood from rotting and warping. Fiberglass windows have good thermal properties but are costly so only account for about one percent of the home window market.
The ENERGY STAR website rates windows with a U-factor number, the lower the number the more effective the window is in preventing heat loss. If you want to know the R-value insulation comparison simply divide 1 by the U-factor so a U-factor value of 0.25 has an equivalent 4 R-value. Window manufacturers have their windows certified with a U-factor by the National Fenestration Rating Council (NFRC) . The entire window is certified for other factors as shown in the sample label at right. To qualify as an ENERGY STAR window in Ohio the U-factor should be equal to, or less than 0.30. Tax credits and local rebates typically require an ENERGY STAR rating.
These are reasons that vinyl is a popular material for frame construction. A high-performance vinyl frame with foam core insulation with heat fusion welding can achieve ENERGY STAR certification. Add an I-beam reinforcement and high quality vinyl and the window will keep its beauty and strength for many years. Vinyl can be manufactured in a variety of colors so you can coordinate the color of the window to the house, and not have to worry about the color of the house to the window.
Included above is a cutaway of a high-performance window with a quality frame. This particular window has a vinyl polymatrix formulation with high-impact modifiers and titanium dioxide. The result is a window with added strength and longer-lasting beauty. A low-quality vinyl is typical among low-priced windows. You can find a variety of these advertised in your local newspapers.
For more information on windows visit the Improveit! Home Remodeling website. These windows are manufactured in Ohio for the Ohio climate. Click on the links below for Part I and Part II of this series on high energy efficient replacement windows.