By Tosha Kelly
Just as a home eventually needs a new roof or new siding, there comes a time when a home needs new windows. Besides the aesthetic boost, replacing old windows can greatly increase a home's energy efficiency. In fact, if you have a home with inefficient windows, you could be throwing 30 percent of your heating dollars right out the window.
But with all the options in heat-reflective glass and framing materials, how do you make the right choice? Here are some guidelines to see you through the process.
All glass may look the same, but different types offer varying degrees of energy efficiency and protection from the elements. With the right glass, your house – and your utility bills – will be much more comfortable.
"Energy efficiency is one of the top demands from homeowners today," says Brian Hedlund, Jeld-Wen Windows & Doors product marketing manager. "While the amount of savings varies depending on the type of window, the number of windows and other factors, a typical household in Alaska can save between $385 and $490 per year on utility bills just by replacing single-pane windows with Energy Star-qualified windows. Because energy efficient windows reduce heat buildup in the summer and reduce heat loss in the winter, energy costs are lower year-round."
Single-pane windows don't provide much insulation against cold or hot temperatures. Double-pane windows have an air space, typically one-half to one inch, sandwiched between two sheets of glass to provide an extra layer of insulation. If the space is too narrow, temperature is too easily conducted. If the space is too wide, convection currents are created that transfer heat or cold. A half-inch air space is optimal thermal air space between each layer of glass, says Walt Murphy, Capitol Glass and Northerm Windows general manager.
Triple-pane windows aren't as popular as they used to be, mainly because the extra layer of glass adds significantly to the weight and cost while only marginally improving the efficiency. In addition, triple-panes are very heavy and require thicker framing to support their weight, which means less light and view.
Today's double-panes can provide a comparable level of energy efficiency, especially those with advanced low-E coatings. This coating is a transparent metallic layer applied to one surface of insulating glass, says Jeld-Wen's Hedlund. "In the winter, low-E reflects some of the interior heat back into the home. And in the summer, it reduces the amount of the sun's heat entering the home."
Low-E glass also blocks harmful UV rays, says Hedlund. Without UV protection, powerful sunlight can cause fading and discoloration to sofas, rugs, artwork and other home accessories. Laminated glass, too, will reduce UV transmission by 99.9 percent, says Larry Phelps, Alaska sales representative for Pella Windows & Doors. "It's a polyvinyl inner layer in between two pieces of glass."
In most double-pane windows, regular air trapped between the glass provides the insulation. In better double-panes, the space is filled with an inert argon gas blend. Argon is about five times the density of air, making the window better at resisting heat flow and better at insulating.
"What's important for our climate up here is what's called 'warm edge'," explains Phelps. "'Warm edge' refers to the type of spacer material used to separate the panes of glass (or glazing) in an insulated window unit. If the material conducts less heat or cold than a conventional aluminum spacer at the edge of the glass, it is said to be warm edge. Most of these newer window spacers are less conductive and outperform pure aluminum.
"We use an Edgetech Super Spacer," says Murphy of Capitol Glass and Northerm Windows. The Super Spacer is designed to minimize the loss of heat through the edge of the insulated glass unit, "It goes between the glass," Murphy explains. "There's no metal, so it doesn't conduct any cold and it gives you a warmer edge of glass." The temperature at the edge of the glass on an aluminum spacer, for example, can be around 25 degrees; the Super spacer is around 42 degrees – a difference of 17 degrees. Condensation is also greatly reduced, even in environments where the humidity can reach as high as 50 percent.
To help make window shopping easier, look for glass that is rated by the National Fenestration Rating Council, an organization that sets industry standards and ratings. You'll want to select windows that have an NFRC label with a low U-factor. The lower the U-value, the greater a window's resistance to heat flow and the better its insulating value. Most windows rate between 0.20 and 1.20. For northern climates, select windows with a U-factor of 0.35 or less.
If you're going to invest money in good window glass, you want the frame to be just as good. A variety of materials are available, and you should be aware of the pros and cons of each. Here's a comparison of the most common options.
PROS: Wood is a beautiful option that can enhance curb appeal. It's also easily customized, and can match virtually any architectural style you desire. A good wood window is a piece of furniture in the home, says John Kirchner, public relations manager of Integrity Windows & Doors. "You can paint and stain it to match the décor of your home, and wood is a naturally insulating material, which makes it an energy efficient product."
Wood is the traditional window frame material because of its availability and ease of milling into the complex shapes required to make windows, according to Efficient Windows Collaborative.
"Usually the frames are where the heat is lost," says Nils Petermann, project manager of the Collaborative. Wood frames are good because they don't leak a lot of heat.
CONS: However, when it comes to high rise buildings, or special climate conditions, wood isn't as strong. "You need that strength to make sure the material doesn't contract or expand," Petermann says, "and it's more susceptible to rot."
PROS: Vinyl is a great choice for homeowners looking for affordable, reliable and efficient windows, but who may not have a budget for custom wood windows. Vinyl provides an attractive look and is low maintenance, which is an important factor for buyers. Vinyl frames are also undergoing some major advancements when it comes to having detailed styling options, says Hedlund of Jeld-Wen Windows & Doors.
Vinyl is a very versatile plastic with good insulating value and moisture resistance. You don't have to paint it because the color goes all the way through, so there is no finish coat that can deteriorate over time or get damaged. Some vinyl window manufacturers are now offering surface treatments like laminates and coatings. Plus, recent advances have improved vinyl's stability and resistance to damage from sunlight and temperature extremes.
In terms of thermal performance, vinyl frames are comparable with wood, while there are minor differences, depending on the frame construction. A small, hollow chamber within the frame reduces convection exchange, as does adding an insulating material.
"Overall, vinyl is the preferred choice for the majority of windows – new construction and replacement – primarily due to vinyl's low maintenance and energy efficiency," according to Hedlund. The company says vinyl frames make up more than half of windows sold in 44 states.
CONS: "Vinyl is not as strong and durable (as fiberglass) and generally won't last as long," says Kirchner of Integrity Windows & Doors. "It will fade and discolor. It's a petroleum-based product, so it's not necessarily 'green.'"
PROS: A composite window frame is made from more than one kind of material. This allows the manufacturer to make the material fit the task. For example, the inside surfaces of the window frame might be made from wood, so it could be painted or stained. The outside surface, however, could be made from a more weather-resistant material like vinyl or aluminum. The classic example of this is a wood window frame with vinyl or aluminum cladding. A newer type of composite window has exterior parts that are made from a blend of wood chips and recycled plastic.
"In terms of durability and maintenance, composite frames have some advantages," says Petermann.
Renewal by Andersen Windows, for example, uses a maintenance free frame made from Fibrex, an innovative material consisting of 40 percent wood and 60 percent thermoplastic polymer by weight. Fibrex material is a good insulator and has the strength and durability of wood but won't rust, rot or peel. Also, these wood/plastic blends can be painted, without being susceptible to rot when the paint wears.
CONS: Kirchner says composite windows may expand and contract. They are less energy efficient over the long term and less durable than fiberglass.
PROS: Hedlund says aluminum window frames are recognized for their affordability and durability. Aluminum is typically the least expensive choice and is generally selected for price. Aluminum window frames are light, strong, durable, and easily extruded into the complex shapes required for window parts. They're available in anodized and factory-baked enamel finishes that are extremely durable and low-maintenance. "Aluminum is a higher conducting material, and you don't have as much condensation," says Petermann of Efficient Windows Collaborative.
CONS: Aluminum frames are not as energy efficient as wood or fiberglass and they don't have the same beauty, says Kirchner. The biggest disadvantage of aluminum is that in cold climates, a simple aluminum frame can easily become cold enough to condense moisture or frost on the inside surfaces of window frames.
PROS: Fiberglass is eight times stronger than vinyl and twice as strong as steel, says Kirchner. It's very low maintenance and green for a number of reasons. Fiberglass is made from sand, so it's an abundant source. And since it's made of the same material as glass, it will expand and contract at the same rate. "You're gonna have less seal failure," he says.
According to Efficient Windows Collaborative, fiberglass frames are dimensionally stable and have air cavities. When the cavities are filled with insulation, fiberglass frames have thermal performance superior to wood or vinyl.
CONS: Often, there are fewer choices available in fiberglass. "They don't have the look of a wood window and there are fewer color options," adds Kirchner.
A great way to find the right products for your home is to look for the Energy Star symbol. Energy Star-qualified windows are twice as efficient as the average window manufactured just 10 years ago. Your investment will pay for itself over time, and then the savings is money in the bank every year.