Sustainable Living: Windows of Opportunity

Living Room windows
Photograph provided by MGE

While new windows enhance your home’s aesthetic appeal and can increase its value, they also can improve energy efficiency. It’s an important consideration as heat loss and gain through windows is responsible for up to 30 percent of the energy used for residential heating and cooling.

Understanding different types of windows and materials used in their construction is essential in choosing the right option for your home. From frames to glass, there’s plenty to consider when it comes to looks, upkeep, functionality, and energy efficiency.

Frame of Reference
Many residential windows are made from wood. If you select this option, be sure to check for certification by the Window and Door Manufacturers Association. Wood windows offer good insulating value, but may require more upkeep than other styles. Consider wood windows with vinyl or aluminum cladding on the outer surface because they require less maintenance and don’t need painting. Well-built wood windows can stand the test of time, but they may be more susceptible to mold.

Vinyl frames are a popular style. They’re low maintenance and easy to clean. Sunlight and extreme temperatures used to degrade vinyl, but better vinyl window grades are now available. Look for certification by the American Architectural Manufacturer’s Association. A well-constructed vinyl window can be practical and offer excellent energy efficiency.

Additional frame options include fiberglass, which is stronger than vinyl and can be very energy efficient. Fiberglass frames can also be fabricated to resemble wood. Another option is composite, which combines the strength and stability of wood with the rot resistance and low maintenance of vinyl.

How Many Panes?
Many older homes have single-pane windows, which are made with one pane of glass. A more energy-efficient option is a double-pane window, which consists of two glass panes with an insulating gas between the panes. Double-pane windows offer more layers of protection between the weather and your home.

Double-pane windows made with low-E glass are a good choice for saving energy. This type of glass is coated with a glaze that reflects heat radiation from the sun while still bringing in sunlight. Double-pane windows come in a variety of sizes and styles.

There are also triple-pane windows. Considered more of a luxury product, triple-pane windows are fabricated with three panes of glass. This design increases the amount of insulating space, making them very energy efficient. They also effectively keep out outdoor noise. However, triple-pane windows are costly and quite heavy, which may require modifications to your home’s structure.

Installation is Key
Even the most energy-efficient windows can’t do their job if they’re not installed properly. Be sure to have your new windows installed by trained professionals according to the manufacturer’s instructions. If you do not, your warranty could be void.

Check the Label
Once you decide on the type of windows to purchase, be sure to look for the ENERGY STAR® label. The ENERGY STAR® label indicates a product is independently certified to save energy. Check the label to be sure the windows you’re considering are certified to meet the criteria for your climate. Homes in Wisconsin are in the Northern Climate Zone.

You’ll also see the National Fenestration Rating Council’s (NFRC’s) energy-performance rating on the label. This is similar to the mileage sticker on cars except the lower the NFRC-rated U-factor, the better the energy performance. This rating is the only way to accurately compare the energy efficiency of windows. The solar heat gain coefficient is also listed, which indicates how well a product blocks heat from the sun. In Wisconsin, it may be better to choose windows with a lower solar heat gain for the west and south sides of the house to keep out extra heat during the summer. Windows with a higher solar heat gain could work well on the north and east sides because they let in more of the sun’s light, which heats up your home in the winter.

Update Existing Windows for Energy Efficiency
Keep in mind that buying energy-efficient windows can reduce energy costs, but it takes at least 20 years to recover the cost of the new windows in energy savings. Replacing all the windows in a house rarely saves more than 15 percent of your home’s heating and cooling bill. If your existing windows are in good condition, taking steps to improve their energy efficiency may be the most cost-effective way to increase comfort and save on energy costs.

• Use window shades strategically. During the cooling season, sun that shines on your windows heats up your home. Close window coverings to reduce heat gain. During the heating season, open window coverings to take advantage of natural light and heat from the sun.

• Lock up. When heating or cooling your home, don’t just shut your windows—lock them as well. This step can be overlooked, but is very important. The locking mechanism activates a seal that helps keep the air you heat or cool stay inside your home.

• Check for air leaks, then consider a window film to eliminate drafts. Be sure a full seal is made with the frame of the window. If there’s even a small hole or area that isn’t sealed, it will diminish the effectiveness of the covering. Another option is a temporary caulk that peels off when you want it off.

Ask the Experts
Window shopping can be complicated. MGE is available to answer your questions and provide tips on new windows as well as making existing windows more energy efficient. MGE’s energy experts are available 8:00 a.m. to 4:30 p.m., Monday through Friday, at 608.252.7117. Or you can email .

Other Resources

Energy Efficiency Kit


Focus on Energy

MGE Connect