Energy-Efficient Window Glazing
Life on the edge
More than just cold air, condensation and moisture are key to poor window performance or failure. Moist conditions promote mold growth, foster rot and decay, and contribute to paint failure. Condensation is the most frequent reason window professionals are asked to return. To be sure, climate will affects your home window.
The edges of a multiple-glazed window are the coldest parts, and that's where condensation forms first and most frequently. Cold edges are even more of a problem with true divided-lite windows. (A lite is a pane.) That's because each individual pane has edge spacers. In true divided-lite windows, the ratio of cold edge to warm center is higher than it is with regular insulated windows. Therefore, warm edges are key to reducing the likelihood of condensation, and improving the efficiency and longevity of your windows.
Energy-Efficient Window Glazing
Edge spacers are made from different materials, and the material makes really affects the rate heat travels through a window's edge. Aluminum spacers are not recommended. Less conductive materials are plastic, foam, rubber, and thin stainless steel. Many manufacturers now offer these 'warm edge spacers' as standard features.
If improving energy efficiency (and the value of your investment) is a major goal, make sure the windows you purchase have warm edge spacers. Warm edge spacers can make an enormous difference in your window's performance. They can increase edge temperature by roughly 5 degrees and improve the U-value by 10%, reducing condensation and enhancing your window's energy efficiency.
The Importance of a Frame
It may sound overly simple, but it's key to everything: Good frames insulate. Although vinyl frames are increasingly grabbing bigger shares of the market, wood still accounts for about half of all available windows (and that includes vinyl- and aluminum-clad wood frames).
Hollow vinyl frames are next, and their affordability accounts for their explosive rise in popularity, followed by aluminum. Wood-resin composites, PVC foam, insulated vinyl, fiberglass, and other alternative materials represent much smaller percentages of the market, but they, too, are slowly making inroads with consumers.
The frame itself represents about 25% of a window's total area, so it's vitally important that the frame be thermally nonconductive. Generally, wood and vinyl are the best performers (with similar U- values), which explains why they are the market leaders. Aluminum frames are much poorer performers in comparison.
Wood frames are usually more expensive, and they offer many benefits. It looks good, is a natural and renewable material, and can easily be repainted or restained (and you can change the frame's color as often as the mood strikes).
On the other hand, maintenance is more of an issue with solid wood frames than with any other frame material. Wood is susceptible to the elements and to pests wood swells and contracts, can rot and mold, and is attractive to termites and other insects. Paint is also more likely to fail. (If you want to change colors, however, that might just be the impetus you need.)
If you're considering wood frames, another option is a clad version. You could even get wood frames that are clad on the exterior side only, so that you can experience the beauty of a wood frame inside. Clad versions are much easier to maintain, but restrict your flexibility when it comes to changing the color of your window frame. An exterior only clad frame does give you the option of changing the color of your interior frame, however.
Whether you choose a solid or clad wood frame, make sure that the manufacturer has treated the wood with water-repellant preservatives. This will extend the life of your frame by improving its durability, paint retention, and dimensional stability.
Making Good Connections
Areas where the frame joins together absolutely must be tightly sealed. A good seal will keep water and air out and improve your window's efficiency. Testing a window in a retail location is fine, but you need to have some idea how a window will perform after being opened and closed hundreds of times, getting wet in storms, dried by the sun, and enduring freezing winter temperatures. The weatherstripping needs to provide a tight seal even after all of that!
Flimsy, low-quality, inexpensive plastic, metal, or brushlike materials won't last. The best solution is to use compressible gaskets, like those used to seal car doors. Closing a window must really, truly close it up tight!
Windows are a considerable investment. Check all the components of a window, and investigate performance ratings (like U-values). Look into consumer ratings as well. Ask your contractor or installer about a brand's track record. Don't experiment choose proven winners.