Windows provide our homes with light, warmth, and ventilation, but they can also negatively impact a home's energy efficiency. You can reduce energy costs by installing energy-efficient windows in your home. Some energy efficiency improvements to existing windows can also help.
Here you'll find information about how to do the following:
When properly selected and installed, energy-efficient windows can help minimize your heating, cooling, and lighting costs.
Achieving improved window performance in your home involves three steps:
Before selecting windows for your home, you need to determine what types of windows will work best and where to improve your home's energy efficiency.
First, it's a good idea to understand the energy performance ratings of windows if you don't already. Then, you can determine what energy performance ratings you need for your windows based on your climate and home's design.
For labeling energy-efficient windows, ENERGY STAR® has established minimum energy performance rating criteria by climate. However, this criteria doesn't account for a home's design, such as window orientation. For more information, see passive solar window design.
If you're constructing a new home or doing some major remodeling, you should also take advantage of the opportunity to incorporate your window design and selection as an integral part of your whole-house design—an approach for building an energy-efficient home.
You'll find that you have several options to consider when selecting what type of windows you should use in your home.
When selecting windows for energy efficiency, it's important to first consider their energy performance ratings in relation to your climate and your home's design. This will help narrow your selection.
A window's energy efficiency is dependent upon all of its components:
A window frame can conduct heat, contributing to a window's overall energy efficiency, particularly its U-factor.
There are advantages and disadvantages to all types of frame materials. Overall, vinyl, wood, fiberglass, and some composite frame materials provide greater thermal resistance than metal.
Although very strong, light and almost maintenance free, metal or aluminum window frames conduct heat very rapidly. Because of this, metal makes a very poor insulating material. To reduce heat flow and the U-factor, metal frames should have a thermal break—an insulating plastic strip placed between the inside and outside of the frame and sash.
Composite window frames consist of composite wood products, such as particle board and laminated strand lumber. These composites are very stable, they have the same or better structural and thermal properties as conventional wood, and they have better moisture and decay resistance.
Fiberglass window frames are dimensionally stable and have air cavities (similar to vinyl). When these cavities are filled with insulation, they offer superior thermal performance compared to wood or vinyl (similar to insulated vinyl frames).
Vinyl window frames are usually made of polyvinyl chloride (PVC) with ultraviolet light (UV) stabilizers to keep sunlight from breaking down the material. PVC is a very versatile plastic with good insulating value. Vinyl window frames also do not require painting and have good moisture resistance. However, at high temperatures, they may expand and warp; at extremely low temperatures, they may crack. Also, if sunlight hits the material for many hours a day, colors other than white may tend to fade over time.
Insulated vinyl frames are also available. Unlike standard vinyl frames, their hollow cavities are filled with insulation. This makes them thermally superior to standard vinyl and wood frames. Usually these high-performance frames are used with high-performance glazings.
Wood window frames insulate well, but they also expand and contract according to weather conditions. They can also be quite heavy and thicker than other frames. This can make storage difficult, reduce the view out the window, and reduce the amount of natural light in the room. Wood frames also require the most maintenance. There are, however, aluminum- or vinyl-clad wood frames that reduce maintenance requirements.
When selecting windows for your home, it's important to consider what type of glazing or glass you should use to improve your home's energy efficiency. Based on variouswindow design factors—such as window orientation, your climate, your building design, etc.—you may even want different types of glazing for different windows throughout your home.
There are many types of glazing available for windows, especially since many glazing technologies can be combined. These window glazing technologies include the following:
When selecting windows for your home, it's also important to consider how they're operated. Some operating types have lower air leakage rates than others, which will improve your home's energy efficiency.
There are numerous window operating types to consider. Traditional types include the following:
Hinged at the top and open outward. Because the sash closes by pressing against the frame, they generally have lower air leakage rates than sliding windows.
Hinged at the sides. Like awning windows, they generally have lower air leakage rates than sliding windows because the sash closes by pressing against the frame.
Fixed panes that don't open. They're airtight but not suitable in places where window ventilation is desired.
Hinged at the bottom and open inward. Like both awning and casement, they generally have lower air leakage rates because the sash closes by pressing against the frame.
Both sashes slide vertically in a double-hung window. Only the bottom sash slides upward in a single-hung window. These sliding windows generally have higher air leakage rates than projecting or hinged windows.
Both sashes slide horizontally in a double-sliding window. Only one sash slides in a single-sliding window. Like single- and double-hung windows, they generally have higher air leakage rates than projecting or hinged windows.
Even the most energy-efficient window must be properly installed to ensure that its energy performance is achieved and that it does not contribute to a home's moisture problems. Therefore, it's best to have a professional install your windows.
Window installation varies depending on the types of the following materials:
Windows should be installed following manufacturing recommendations, along with the following additional guidelines (primarily for windows with fin mounting systems).
The window opening must be flashed and integrated into the home's weather-resistive barrier so that any potential water leaks do not cause damage. A weather-resistive barrier is a drainage plane that allows water that has penetrated past the siding to drain away from the wall system. Details will vary with siding, window type, the installation sequence for the window, trim, and weather-resistive barrier. It is advisable to install window head and sill flashing, whether it is metal, plastic, or a self-sticking, elastomeric membrane. Avoid relying on tapes or sealants to provide waterproofing, as these products may fail over time.
It's common practice and recommended by some manufacturers to cut an "X" in housewrap placed over window openings, pull the material inside, and secure it by stapling. Other manufacturers require alternative methods, such as the modified "I"-cut, depending on the overall flashing approach. The "I"-cut allows the vertical leg of the head flashing to be placed under the weather-resistive barrier and then taped or sealed.
It's best to divert drainage onto the face of the weather-resistive barrier. Do not tape down or seal behind the bottom nailing flange of the window, as doing so could accidentally trap in water.
Windows must also be properly air sealed during installation to perform correctly. To air seal the window, caulk the backsides of the window mounting flanges (top and sides only) to the weather-resistive barrier during installation. The mounting flange (nailing fin) is an integral part of most window frames that laps over the conventional stud construction. Nails are driven through it to secure the frame in place. Also, from inside the house, seal the gap between the window frame and rough opening using backer rod and caulk or non-expanding latex-based spray foams that will not pinch jambs or void window warranties. Backer rod is a closed-cell foam or rope caulk that is pressed into cracks or gaps with a screwdriver or putty knife. Insulation stuffed into this crack does not stop air flow.
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