Windows are responsible for 25%–30% of residential heating and cooling energy use and are an important consideration for both new and existing homes.
If you are selecting windows for new construction, it's important to choose the most efficient windows you can afford that work best in your climate.
About 40% of residential windows on existing homes in the United States are single-pane windows. If your existing windows are single pane, taking steps to reduce the energy loss through windows can make your home more comfortable and save you money on energy bills.
You have three broad options if you hope to reduce the amount of energy lost through your windows and improve the comfort of your home:
1. Improve the efficiency of your windows
2. Retrofit your windows
3. Replace your windows.
Improving the Efficiency of Your Windows
If your windows are in good condition, taking steps to improve their efficiency may be the most cost-effective option to increase the comfort of your home and save money on energy costs. There are several things you can do to improve the efficiency of your existing windows:
Cold Weather Window Tips
- Use a heavy-duty, clear plastic sheet on a frame or tape clear plastic film to the inside of your window frames to reduce drafts.
- Install tight-fitting, insulating window shades on windows that feel drafty after weatherizing.
- Close your curtains and shades at night to protect against cold drafts; open them during the day to let in warming sunlight.
- Install exterior or interior storm windows, which can reduce heat loss through the windows by approximately 10%-20%, depending on the type of window already installed in the home. They should have weatherstripping at all movable joints; be made of strong, durable materials; and have interlocking or overlapping joints.
- Repair and weatherize your current storm windows, if necessary.
Warm Weather Window Tips
- Install white window shades, drapes, or blinds to reflect heat away from the house.
- Close curtains on south- and west-facing windows during the day.
- Install awnings on south- and west-facing windows.
- Apply sun-control or other reflective films on south-facing windows to reduce solar heat gain.
Selecting New Energy-Efficient Windows
Before selecting new windows for your home, determine what types of windows will work best and where to improve your home's energy efficiency. It's a good idea to understand the energy performance ratings of windows so you’ll know what energy performance ratings you need for your windows based on your climate and the home's design.
For labeling energy-efficient windows, ENERGY STAR® has established minimum energy performance rating criteria by climate. However, these criteria don't account for a home's design, such as window orientation.
Windows are an important element in passive solar home design, which uses solar energy at the site to provide heating, cooling, and lighting for a house. Passive solar design strategies vary by building location and regional climate, but the basic window guidelines remain the same—select, orient, and size glass to maximize solar heat gain in winter and minimize it in summer.
In heating-dominated climates, major glazing areas should generally face south to collect solar heat during the winter when the sun is low in the sky. In the summer, when the sun is high overhead, overhangs or other shading devices prevent excessive heat gain.
To be effective, south-facing windows should have a solar heat gain coefficient (SHGC) of greater than 0.6 to maximize solar heat gain during the winter, a U-factor of 0.35 or less to reduce conductive heat transfer, and a high visible transmittance (VT) for good visible light transfer. See Energy Performance Ratings to learn more about these ratings.
Windows on east-, west-, and north-facing walls should be minimized while still allowing for adequate daylight. It is difficult to control heat and light through east- and west-facing windows when the sun is low in the sky, and these windows should have a low SHGC and/or be shaded. North-facing windows collect little solar heat, so they are used only for lighting. Low-emissivity (low-e) window glazing can help control solar heat gain and loss in heating climates.
In cooling climates, particularly effective strategies include preferential use of north-facing windows and generously shaded south-facing windows. Windows with low SHGCs are more effective at reducing cooling loads.
Some types of glazing help reduce solar heat gain, lowering a window's SHGC. Low-e coatings—microscopically thin, virtually invisible metal or metallic oxide layers deposited directly on the surface of glass—control heat transfer through windows with insulated glazing. Tinted glass absorbs a large fraction of incoming solar radiation through a window, reflective coatings reduce the transmission of solar radiation, and spectrally selective coatings filter out 40% to 70% of the heat normally transmitted through insulated window glass or glazing, while allowing the full amount of light to be transmitted. Except for spectrally selective, these types of glazing also lower a window's VT. See Window Types to learn more about glazing, coatings, tints, and other options when selecting efficient windows.
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.
Retrofitting your windows involves adding more permanent features to improve the efficiency of your windows.
Depending on the condition of the windows and the retrofitting needs, the following may be part of a retrofit plan:
Adding storm windows or panels
Adding solar control film
Adding exterior shading, such as awnings, exterior blinds, or overhangs.
With any retrofit, it is important to ensure proper installation and air tightness. Following the retrofit, you may want to take additional steps to ensure efficiency by caulking and weatherstripping and adding window coverings and treatments.
Retrofit Your Windows
Even the most energy-efficient window must be properly installed to ensure energy efficiency. Therefore, it's best to have a professional install your windows.
Window installation varies depending on the type of window, the construction of the house (wood, masonry, etc.), the exterior cladding (wood siding, stucco, brick, etc.), and the type (if any) of weather-restrictive barrier.
Windows should be installed according to the manufacturer’s recommendations and be properly air sealed during installation to perform correctly. To air seal the window, caulk the frame and weatherstrip the operable components.
- Complete Window and Frame Replacement - Building America Solution Center
- ENERGY STAR Residential Windows, Doors and Skylights
- Energy Performance Label for Windows, Doors, and Skylights - National Fenestration Rating Council
- Efficient Windows Collaborative
- Climate Zone Recommendations
- Windows and Daylighting - Lawrence Berkeley National Laboratory
- Window Selection Tool
- Window Technologies: Low-E Coatings