No matter if your goal is to retain heat, block it, or both – depending on the time of year – selecting the correct windows can significantly reduce energy consumption and make it more economical to maintain a comfortable temperature in your home.
When it comes to energy efficiency, several factors influence a window’s performance, including its type, the glass construction, and accessory choices like grilles. We’ll outline what to prioritize to choose the most energy-efficient windows for your residence, including considerations for specific climates.
How to Select an Energy-Efficient Window
The straightforward answer to choosing an energy-efficient window is to opt for the more efficient window styles—casement, awning, or picture windows—paired with the most insulating glass construction (triple-pane glass) and glass coatings best suited to your local climate. However, your climate, aesthetic preferences, and budget will all play a role in the final decision. Continue reading for a deeper understanding of what your optimal energy-efficient window solution might be.
Which Window Types Are Most Efficient?
Not all window styles offer equal energy efficiency. For superior performance, focus on casement, awning, and picture windows. Casement and awning windows feature a single sash, in contrast to double-hung windows, which have two. The combination of their simpler design and a seal that tightens when wind presses against them contributes to their higher energy efficiency. The most efficient windows of all are picture windows because they are fixed and do not open.
Did you know? If you appreciate the aesthetic of a double-hung window but require a more energy-efficient alternative, there are clever visual tricks. You can incorporate grilles in such a way that a casement window mimics the appearance of a double-hung, as shown in the image above. It’s important to note that if grilles are positioned between the glass panes and make contact with the glass (known as full divided light), they can facilitate energy transfer between indoors and outdoors, thereby diminishing efficiency. An excellent solution for this is the energy spacer bar available with the A-Series. Its ingenious design provides an authentic look while boosting performance, as it avoids direct contact with the glass.
What Defines Double-Pane and Triple-Pane Windows?
Glass construction is a pivotal component of energy efficiency. Both the number of glass sheets (panes) in a window and the air space between them are crucial. Here’s what you need to understand:
- Single-pane glass consists of just one sheet of glass separating the indoors from the outdoors. This type of window glass is often found in older homes. While it can possess significant charm, particularly when featuring leaded glass, it lacks energy efficiency. This is why single-pane windows are frequently supplemented with exterior storm windows for additional insulation.
- Double-pane, or dual-pane glass, incorporates two sheets of glass with an airspace in between. This airspace in our windows is typically filled with an argon-gas blend, which is denser than air and consequently improves insulation.* This glass type offers superior insulation compared to single-pane glass and is a standard feature on all our windows, as well as being mandated by most building codes.
- Triple-pane glass takes efficiency a step further by including an additional pane of glass and airspace, making it the most energy-efficient glass type available. In fact, A-Series triple-pane windows are recognized as ENERGY STAR® Most Efficient and are certified to meet the stringent energy efficiency standards required by Phius (Passive House Institute US). Triple-pane glass is an optional upgrade for our A-Series and E-Series windows.
Dual-pane glass features two sheets of glass with an insulating airspace between them. Triple-pane glass adds an extra airspace and a third sheet of glass, rendering it the most efficient glass type. Andersen® windows come standard with dual-pane glass, with triple-pane glass available as an option on A-Series and E-Series windows.
Speak Like a Pro: Thermal Performance
In simple terms, thermal performance refers to how effectively your window retains heat (or energy) within your home. To delve deeper, the U-Factor is the metric used to determine how well a window or door prevents heat from escaping. A lower U-Factor indicates less heat loss. Understanding U-Factor values is invaluable when comparing window brands.
For the most accurate assessment of performance, it’s critical to consider the U-Factor value for the entire window (termed “whole unit performance”), rather than just the center of the glass, which is a measurement you might encounter. When comparing performance across different manufacturers, always ensure you are evaluating “whole unit performance” for all products.
What is a Low-Emissivity Glass (Low-E) Coating?
One effective way to optimize windows for specific climate zones is through the application of a glass coating. Low-E glass coatings are standard on our windows. These ultra-thin, generally transparent coatings are applied in various configurations to enhance your home’s comfort. They function by reflecting or absorbing heat. Furthermore, different coatings can be combined and applied to different panes of glass to achieve optimal performance by selectively reflecting and absorbing heat as required.
This adaptability is another advantage of dual- and triple-pane windows. Indeed, one reason triple-pane windows offer such superior performance is that the third pane provides an additional opportunity to incorporate another Low-E coating. Here’s what you need to know:
Low-E coatings for cold climates:
Low-E4® glass is a suitable option for most climates, including those with four distinct seasons, as it helps block heat in warm months and retain it during cold months. Depending on specific conditions, it might be beneficial to consider a coating designed to help warm the home in winter, or one that offers additional protection from intense sun. Consider the following options:
- SmartSun™ glass provides the benefits of Low-E while also blocking 95% of harmful UV rays, which helps prevent fading of your furnishings and décor. This option is available across all our products.
- PassiveSun® glass is engineered for climates where significant heating is required. It allows you to maximize the sun’s warmth for heating your home and is available on all our products.
- HeatLock® technology is designed for the northernmost climates. It creates a barrier that helps keep warming rays from the sun inside and performs best in homes equipped with whole-house air exchangers or dehumidifiers. It’s available on most of our products.
The combination of PassiveSun glass with HeatLock technology can be highly effective in a Northern climate, as it aids in insulating the home while also harnessing solar energy for heating. This pairing could be particularly useful in homes designed according to passive house principles.
Low-E coatings for mild to hot climates:
Specific glass coatings are designed to prevent excessive solar heating of your home and even reduce UV ray penetration, including:
- Sun glass is ideal for sunny climates. This coating helps reflect solar heat with a subtle tint that is slightly darker than SmartSun glass.
- SmartSun™ glass is versatile, performing well in both hot and cold climates by providing the benefits of Low-E glass while blocking 95% of harmful UV rays. It can be an excellent choice in the sunny southern and western U.S.
The combination of SmartSun glass with Heatlock technology can be beneficial in mild to hot climates. It aids in insulation while simultaneously reducing heat gained from the sun.
Regardless of your climate, your contractor, builder, or window dealer can help you select the optimal combination of coatings when you place your order.
In a hot, sunny climate, such as Arizona, the right type of glass and glass coatings enable effective management of heat gain while still allowing abundant natural light to enter through large windows and doors like those pictured.
Speak Like a Pro: Solar Heat Gain
Simply put, solar heat gain refers to the amount of warmth a home acquires from the sun. To quantify how much radiant heat enters a home through its windows or doors, a measurement called the solar heat gain coefficient (SHGC) is used. A lower SHGC value indicates less solar heat penetrating the windows. For example, an SHGC of 0.30 means that only 30% of the sun’s energy is passing through the windows into the home. Understanding such metrics can be useful when comparing windows across different brands. And just as with U-Factor values, you’ll want to ensure you’re reviewing the “whole unit performance” rather than just the center of the glass, to accurately assess performance and compare products from various manufacturers.
Other Factors Influencing Energy Performance
As you’ve undoubtedly gathered, windows can be highly customized for energy-efficient performance in numerous ways. Two additional selections that can significantly impact performance are grilles and breather tubes. While you can opt to omit grilles or choose a more energy-efficient design (as discussed below), breather tubes are typically mandatory at high altitudes. However, if you are aware of the effect these features have, you can make other selections to counteract their impact on overall performance.
- Grilles: When these ornamental bars make contact with both panes of glass, they reduce efficiency by conducting energy and diminishing the insulating power of the airspace. This is precisely why the energy spacer bars available with A-Series windows and doors were designed to avoid touching the glass. They are an excellent option if you desire the authentic appearance of full divided light grilles. However, the most energy-efficient choice of all is to forgo grilles entirely.
- Breather tubes: At elevations above 4,000 feet, these tubes are essential. They prevent windows from becoming over-pressurized by allowing air to escape from the space between window panes. Windows manufactured for these higher elevations typically do not include the argon-gas blend usually added to the airspace in our windows, making them inherently less efficient overall. But don’t worry if you reside at high altitude; you can lean into the high-performance selections highlighted above to help improve energy efficiency even when breather tubes are required.
Want to Save Money on Energy-Efficient Windows?
You’ve undoubtedly seen the ENERGY STAR® label on various appliances and products. This label was developed by the U.S. Environmental Protection Agency to simplify the identification of energy-efficient products for consumers. When applied to windows, it signifies that the windows have met specific performance requirements designed to reduce heat transfer within a designated climate zone.
If you replace windows in an existing home with new ones that meet the ENERGY STAR Most Efficient criteria for 2024, you may qualify for a tax credit covering up to 30% of the cost, with a maximum credit of $600 on windows.** This credit is available through 2032 and can also apply to doors. Refer below for the specific criteria by climate zone.
Curious about the meaning of the values mentioned above? Below is an explanation of how these performance measures are interpreted.
Understanding Energy-Efficiency Measures
To secure ENERGY STAR certification for a window or door, a manufacturer must successfully pass independent testing conducted by the non-profit National Fenestration Rating Council (NFRC). The NFRC establishes objective energy performance ratings for windows, doors, and skylights to assist homeowners, builders, architects, and others in making informed purchasing decisions. NFRC testing evaluates and rates a window’s energy efficiency based on several factors, including U-Factor, SHGC, and Visible Transmittance. Here’s how to interpret these measures:
| Metric | What it Measures | Performance Impact | Measurement Ranges |
| U-factor | How well a product prevents heat from escaping | Lower ratings indicate better insulation | Scale of 0-1 |
| Solar Heat Gain Coefficient (SHGC) | The product’s ability to block heat caused by sunlight | Lower ratings signify less heat transfer | Scale of 0-1 |
| Visible Transmittance (VT) | The amount of light allowed through the window | Higher ratings mean more natural light | Scale of 0-1 |