Windows grace your home with beauty and help define its overall style. Beyond their obvious functions of letting in natural light, providing a visual connection to the outdoors, and ventilating your home, windows help control and maintain the desired temperature inside your home by keeping warm air in during the cold months and out during the warm months. According to the U.S. Department of Energy, heat loss and heat gain through windows are responsible for 25 to 30 percent of the energy used to heat and cool your home.
Whether you are building or buying a new home, considering a remodeling project, or just looking to replace your existing windows, it's important to choose the most energy-efficient windows you can afford for your climate. The type of window, the material or materials that make up the window frame, and the type of glazing you choose all influence a window's overall energy efficiency.
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Windows are available in a variety of architectural styles, and your choices are largely a matter of aesthetic preference and the overall style of your home.
Hung windows consist of two sashes, one installed above the other. They can be either single-hung or double-hung. Sashes are the framework that hold the pane or panes of glass together. In hung windows, the sashes slide vertically up and down while remaining in the frame. In single-hung windows, only the bottom sash operates; the top sash remains fixed. In double-hung windows, the sashes can open from either the top or the bottom, offering greater flexibility with ventilation. Hung windows are more often used in traditional-style houses.
Slider windows are essentially single- or double-hung windows turned on their side. One or both sashes glide horizontally along a track over or past the other window. For some, the gliding operation of a slider window is easier to open than the up and down motion of a hung window. Sliders are more often used in modern or contemporary-style houses.
Casement windows are hinged on either the right or left side of the frame. They open outward with a turn of a crank, or in some cases, a push. Casements offer some of the best energy efficiency in windows, thanks to the tight seal that forms when they are closed.
Awning windows are similar to casement windows, but the hinges are located along the top of the frame instead of the side. As a result, the window opens outward and upward. Awnings can be installed above, below, or beside a fixed (non-operable) window and are a good choice for rainy environments because they can let air in while keeping rain out.
Hopper windows are similar to casement windows, but are hinged along the bottom of the frame, so the window opens inward at the top. Hoppers are a good choice for small window applications when you still want ventilation, such as in below-grade basements.
Jalousies are louvered windows, meaning they are made up of many different slats of metal or glass that open like a set of blinds. They are well-suited for warmer climates because they offer some of the best ventilation among window types. All that is required to regulate breezes is a simple adjustment of a rod or crank. Jalousies are not well-suited for colder climates, because they don't provide enough insulation.
Fixed windows cannot be opened but are versatile in that they come in a wide variety of sizes and can be custom-made into just about any shape you want. Picture windows are one type of fixed window. These are usually larger in size with a minimum amount of grillwork to let in the maximum amount of light and offer the best view of the outdoors. When ventilation is not needed, these are a good choice for adding architectural detail to your home. Another type of fixed window is a transom window. Transoms are narrow windows that are often mounted above operational windows or doors to provide extra light while maintaining privacy. Fixed windows are usually found in modern or contemporary-style houses in conjunction with operational windows.
Bay or Bow Windows
Bay and bow windows are similar in that both project outward from an exterior wall of the house, offering more interior space for a window seat or decorative nook. Bay and bow windows differ, however, in the number of windows that make up their complete unit, which, in turn, gives them slightly different shapes. Bay windows are usually made up of three windows: one center window between two windows that are set at 30- or 45-degree angles. A 45-degree bay window pushes out farther and will offer more interior space. Bow windows have 3 to 6 window units attached to each other at 10-degree angles, which results in a gentler curve compared to the angular bay window.
Bay and bow window units are comprised of fixed or operable windows or a combination of the two. In a bay window, for example, the center window is often a larger picture window flanked by two hung or casement windows. Your ability to customize these windows will depend on the brand you choose. Both bay and bow windows will require a roof since they jut out from the side of the house.
Garden (Greenhouse) Windows
Garden windows are like smaller bay windows commonly located over a kitchen sink. They have glass on the front, sides, and top (a "glass roof"). The natural light they let in makes them a great spot for cultivating house plants or starting seedlings.
Skylight windows can either be fixed or operable and can be installed into the ceiling of any room that has straight access to the roof. They fill a space with natural light, but as radiant energy from the sun pours in, they can create problems with heat build-up.
Glass Block Windows
Glass block windows are a good choice when you want to let in natural light and create illusions of space while still maintaining your privacy, such as in a bathroom. Glass block windows are manufactured by attaching blocks to each other side-by-side and in rows. At one time, glass was the only option for these blocks, which meant such windows were very heavy and had to remain fixed. Now, manufacturers are also using acrylic, a type of plastic that is lighter than glass and which may allow for the privacy window to be opened.
Factors to Consider When Purchasing Windows
A number of construction and manufacturing elements should be considering when choosing your windows.
When buying new windows, the window frame is one of the most important factors to consider. A quality frame insulates by sealing out moisture and drafts and can keep a window functioning well for decades rather than years. Window frames can be made from, wood, vinyl, clad wood, aluminum, composites, and fiberglass.
Wood. All-wood frames are the most traditional and have been used on homes for hundreds of years. They are favored by many homeowners for their paintability, their overall energy efficiency, and their warm appearance that complements any architectural style. However, wood frames require a lifetime of maintenance to guard against wood rot and to keep the paint looking fresh.
Vinyl. Vinyl frames are among the least expensive options and are known for being good insulators. They never need to be painted and are virtually maintenance free. Vinyl is not, however, the most durable option because as it responds to changes in temperature, the windows expand and contract, which can lead to seal deterioration and drafts. Vinyl windows should be re-caulked and re-sealed regularly throughout their lifetime.
Clad wood. Clad wood frames are the most popular choice among consumers. Cladding is a protective exterior coating applied to a wood-framed window. There are many types of cladding to choose from, with a range of performance and durability options, but most are made of vinyl, aluminum, or fiberglass. The main benefit of a clad window is that it provides a tough, maintenance-free exterior and a natural-wood interior that you can paint or stain. These advantages mean that clad wood windows usually cost more than solid wood windows.
Aluminum. Aluminum frames are one of the most affordable options for window frames. They are lightweight, strong, and virtually maintenance free. They are also more modern and work well with a modern house style. However, they are not the most efficient when compared to the other options. They conduct heat rapidly, which makes them a poor insulator. Metal frames are best suited for mild climates. If you purchase aluminum windows, make sure they are equipped with a thermal break in the frame—a strip of plastic or rubber that separates the inside from the outside of the frame to help limit heat conductivity.
Composites. Composite frames can be made of wood particles and some are mixed with polymer plastics. They can be painted like wood and are often stronger and more durable than wood. The downside is that these windows are more expensive than the other options.
Fiberglass. Fiberglass frames are stiffer and lighter than wood, as easy to maintain as vinyl, and unaffected by water or temperature changes. On average, costs for fiberglass windows run 25 percent more than vinyl and about half the cost of clad wood. Fewer options exist with fiberglass compared to wood. Fiberglass is more difficult to customize into shapes and there are fewer color and hardware options to choose from.
In addition to choosing a frame type, it is important to consider the type of glazing or glass that will best acheive your home's energy efficiency goals. Based on factors like the direction a window is facing, the climate you live in, and the design of your home, you may even want to select different types of glazing for different window locations.
Most of today's windows are double- or triple-glazed, meaning there are two or three panes of glass that are separated by spacers at the perimeter to establish the distance between the panes and seal the gap. Seals need to be tight to keep the gas between the panes from escaping and to prevent moisture from entering. Filling the area between the panes with a gas minimizes heat transfer between the interior and exterior glazing layers. Argon or krypton—both inert, non-toxic, clear, and odorless_are the gases typically used.
Two numbers to know when choosing glazing are the U-factor and the solar heat-gain coefficient (SHGC). The U-factor measures how well a window stops heat flow. In all climates, the lower the number, the better the performance of the glass. The SHGC measures how much heat enters the home through the window when the sun is shining. Lower numbers mean that less heat is getting in. If you live in a cold climate, you may want windows with a higher SHGC, especially on the south side of your house. The optimal SHGC for each window, determined by your home's climate, orientation to the sun, and any external shading, will likely vary for each window in your home. The U-factor and SHGC numbers appear on the National Fenestration Rating Council (NFRC) label found on most new windows. NFRC reporting standards require U-factors and SHGCs to be whole-window measurements, not glazing-only measurements.
Low-emissivity (low-e) coatings on windows are standard for most North American homes. A low-e coating is an almost invisible layer of metal that the manufacturer applies to one side of the glass to lower the U-factor of the glazing— in other words, to slow heat transfer. Don't assume, however, that because a window is low-e it is good at reducing solar gain. Different types of low-e coatings have been designed to allow for low, moderate, and high SHGC. While windows manufactured with low-e coatings may cost 10 to 15 percent more than regular windows, they reduce energy costs by as much as 30 to 50 percent.
Method of Installation
Knowing how you plan to install your windows will determine whether you purchase new-construction windows or replacement windows.
New Construction. New-construction windows are standard-size windows used primarily when you are building a new house or adding on to an existing house, or sometimes when the frames of existing windows are in such bad shape that the entire window needs to be replaced. New-construction windows can be identified by the nailing fin, a thin piece of metal that extends from the window itself and runs all the way around the perimeter. In new construction, windows are put in before the rest of the wall is finished around it, meaning the nailing fins are nailed directly to the studs and sheathing and are hidden between the interior and exterior walls. As a result, to properly install a new-construction window in an existing home, you would need to expose the studs and sheathing. This is a costly, labor-intensive process, and one that is be nearly impossible to do if your home is made of brick or stone.
Replacement. Replacement windows are custom-sized to fit your existing window openings and are used primarily when replacing a window whose framing is in good condition. Though more carpentry is required, replacement windows can also be used when the existing frame is in such bad shape that it needs to be replaced. There are three levels of replacement windows:
- Sash. A sash replacement leaves the existing frame intact and only replaces the movable parts of the old window. For example, in a double-hung window, the top and bottom sash can be replaced while the frame is left intact.
- Insert. With an insert replacement, a new frame-and-sash window is installed within the existing window frame. This results in a slightly smaller viewing area because the new frame takes up some of the space previously held by the old window panes. This is the most common type of replacement window. Its advantage over sash replacement is that the sash and frame are designed to be compatible with each other.
- Full replacement. In this type of replacement, the old window frame is completely removed and the new window, complete with frame and sash, is installed in the opening. The new window is secured to the wall with screws that blend perfectly into the side of the frame. Having a replacement window that fits the opening exactly is key to ensuring that the window functions at maximum efficiency. To complete the barrier between the inside and the outside, the new replacement windows are caulked and the edges of the window frame are trimmed.