How Do Energy-Efficient Windows Work?
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If replacing your windows is on your home improvement to-do list, consider windows that help you save energy. Energy-efficient windows can improve home comfort, lower energy bills, and reduce your carbon footprint.
In this guide, we’ll discuss energy performance ratings and the qualities of energy-efficient windows to help you choose windows that meet your needs.
What Makes a Window Energy-Efficient?
Energy-efficient windows are made of materials that have insulative properties or block UV rays. In comparison to traditional windows, energy-efficient windows typically have a combination of several of the following features:
- Double- or triple-pane glass: These windows fuse two or three glass panels to provide a more substantial barrier than single-pane windows, keeping temperature-controlled air in while preventing outdoor air from entering.
- Insulated frames: Fiberglass window frames have air cavities you can fill with insulation to enhance their thermal performance compared to other options, such as wood windows.
- Insulating gas fills: Double- and triple-pane windows have insulating gas—such as argon or krypton—between the panels to help keep them closer to room temperature.
- Low-emissivity glass coatings: Low-e glass is treated with a coating that filters the amount of UV light entering your home. It keeps heat out in the summer and in during the winter.
- Warm edge spacers: Spacer systems between double and triple panes of glass are designed with materials that reduce condensation buildup and seal in escaping heat.
Understanding Energy Performance Ratings
Energy performance ratings from the National Fenestration Rating Council (NFRC) and Energy Star can help you understand which windows conserve energy. The NFRC tests, certifies, and labels windows, doors, and skylights based on their energy performance ratings. Energy Star bases its qualifications on U-factor and solar heat gain coefficient (SHGC) ratings.
The following metrics measure the heat transfer rates and insulation properties that make windows energy-efficient.
Air Leakage
Air leakage (AL) refers to the rate of air movement around a window when there’s a pressure difference across it. Windows with a low AL rating are tighter than those with a high rating, assuming proper installation.
Condensation Resistance
Condensation resistance (CR) measures the performance of parts of the window assembly through different temperatures and humidity levels on a scale from 1–100.
Solar Heat Gain Coefficient
The SHGC measures how much solar radiation passes through a window. The lower the SHGC, the less solar heat it transmits. Lower numbers are ideal for hot climates to minimize heat gain, while higher numbers are better for cold climates to allow more passive solar heating.
U-Factor
The U-factor is the rate of nonsolar heat transfer through your window. While some U-factor ratings refer to just the glass or glazing, NFRC U-factor ratings represent the entire window performance. U-factor ratings are measured on a scale typically ranging from 0.20–1.20, with lower U-factor ratings indicating better insulating performance. The optimal U-factor rating for your replacement windows depends on your climate, as follows:
- Colder climates: Less than or equal to 0.30
- Hot climates in the South that are cooling dominated: Less than or equal to 0.60
- Mixed climates in the North and Midwest: Less than or equal to 0.32
- Mixed climates in the South and Central regions: Less than or equal to 0.35
Visible Transmittance
Visible transmittance (VT) is a fraction of the visible spectrum of sunlight transmitted through a window’s glazing. Determine the VT you need for your window based on your home’s daylighting requirements and whether you need to minimize interior glare.
Types of Energy-Efficient Windows
Energy-efficient windows are available in several window types and styles. A window’s functionality can impact your home’s energy use. Here are some popular window types:
- Awning and hopper windows: Awning windows are hinged at the top and open outward, while hopper windows are hinged at the bottom and open inward. These window types have lower AL ratings because the sash closes by pressing against the frame.
- Bay and bow windows: Bay and bow windows join a combination of windows to create a curve, introducing more light and airflow into your home. These windows’ energy efficiency depends on their size and how the side windows operate.
- Casement windows: Hinged at the sides, casement windows are similar to awning windows in that the sash closes by pressing against the frame to reduce air leakage.
- Double-hung windows: In a double-hung window, both sashes slide vertically, resulting in higher AL ratings than hinged windows.
- Picture windows: Picture windows are stationary windows that don’t open. They are sealed directly in the frame, making them energy-efficient by design when installed correctly.
- Sliding windows: In a double-sliding window, both sashes slide horizontally, resulting in higher AL ratings than hinged windows.
Cost per Window
The cost of energy-efficient windows ranges widely and depends on window size and materials. Here are the average cost ranges of the window types we discussed above:
- Picture: $65–$700
- Double-hung: $150–$650
- Hopper: $150–$650
- Sliding: $150–$800
- Casement: $150–$1,000
- Awning: $400–$850
- Bay: $900–$7,100
- Bow: $1,500–$6,500
Cost data was sourced via Angi.
Choosing Energy-Efficient Windows
Carefully examine your climate and energy efficiency goals and compare various window materials and certifications to choose the best energy-efficient windows for your home. Consider the following tips:
- Compare the energy performance ratings of different window options. Ask dealers and window installation professionals how various window types impact energy efficiency. Compare different styles’ ratings to determine which most likely meets your needs.
- Consider the window style and material that best suits your home. Various window styles have energy-efficient properties that reduce energy consumption. If you dream of sliding windows but are concerned about air leakage, explore options such as low-e coatings and insulated frames.
- Evaluate your climate zone and energy efficiency goals. Your climate determines your heating and cooling needs and optimal energy efficiency ratings. In colder climates, consider selecting gas-filled windows with low-e coatings and a low U-factor. In warmer climates, select windows with coatings that reduce heat gain.
- Get multiple quotes from reputable window installers. Before buying windows, shop around for the best prices and all the features you want. Get multiple quotes and consider installation costs to ensure your new windows’ optimal performance.
- Look for Energy Star and NFRC certifications. Look for Energy Star and NFRC labels to ensure you find windows with the highest energy efficiency ratings. Select windows with ratings that align with your local climate.
- Review warranty coverage and maintenance requirements. Before making a purchase, research different window warranties. Consider what’s covered, how long the warranty lasts, and whether coverage changes over time.
Benefits of Energy-Efficient Windows
Energy-efficient windows provide various benefits. Consider how advantages like lower energy costs, reduced noise, and improved curb appeal will enhance your home.
Better Moisture Control and Less Condensation
Energy-efficient windows keep window temperature aligned with room temperature, cutting condensation on the interior surface of windows. Look for windows with a high CR rating to minimize condensation and maximize moisture control in colder climates.
Enhanced Soundproofing and Noise Reduction
Double- or triple-pane windows designed to improve temperature control have the added benefit of soundproofing. Triple-pane glass is the best option for reducing noise. Since the same technologies to minimize energy consumption also improve soundproofing, the AL rating can help you find the highest soundproofing levels.
Environmentally Friendly With Lower Energy Consumption
Energy-efficient windows reduce the power needed to heat and cool your home, and large windows increase natural light.
Improved Comfort and Reduced Drafts
Energy-efficient windows typically feature double or triple panes insulated with argon or krypton gas to reduce draftiness. Different window types can also reduce draftiness. For example, awning and casement window sashes close by pressing against the frame, preventing air leakage.
Increased Home Value and Curb Appeal
Replacing your home’s windows can add instant curb appeal and increase its value. According to Freddie Mac, homes with high energy efficiency ratings sell for 2.7% more than homes with lower ratings.
Lower Heating and Cooling Costs
Energy-efficient windows use various components to help reduce air conditioning and heating needs. Depending on the windows you’re replacing and your local climate, energy-efficient windows can reduce your energy bills by up to 13%.
Reduced Fading of Furniture and Carpets
Certain window coatings and films designed to reduce UV rays can help reduce furniture and carpet fading without affecting your view. Windows with high VT ratings are most effective at reducing fading.
How Much Can You Save With Energy-Efficient Windows?
The amount you can save with energy-efficient windows varies based on several factors. Understanding these variables can help you estimate your potential return on investment.
Factors Affecting Energy Savings
Several elements influence the energy savings you can expect from new windows, including the following:
- Climate and local energy costs
- Efficiency ratings of new windows compared to old ones
- Size and number of windows replaced
- Your heating and cooling habits
- Your home’s overall energy efficiency
Calculating Return on Investment
Follow these steps to estimate your potential savings:
- Assess your current energy bills.
- Get quotes for energy-efficient window installation.
- Use online energy savings calculators or consult with professionals.
- Consider additional benefits such as improved comfort and increased home value.
While the upfront cost can be significant, many homeowners find that energy-efficient windows pay for themselves over time through energy savings and increased property value.
Maintaining Energy-Efficient Windows for Optimal Performance
Regular care can extend your windows’ lifespans and maintain their energy-saving properties.
Cleaning and Inspection Tips
Routinely perform the following tasks to keep your windows performing at their best:
- Check for condensation between panes, which could indicate seal failure.
- Clean glass and frames regularly with nonabrasive cleaners.
- Inspect weatherstripping and seals annually for wear or damage.
- Lubricate moving parts as recommended by the manufacturer.
When To Consider Replacement
While energy-efficient windows have long lives, they may eventually need replacement. Signs it’s time to consider new windows include the following:
- Difficulty opening or closing
- Excessive condensation or fogging between panes
- Increased energy bills despite proper maintenance
- Visible damage or warping
Regular inspections can help you identify these issues early, allowing you to plan for replacement before energy efficiency is significantly compromised.
Our Conclusion
Energy-efficient windows provide substantial benefits. They’ll help you save money on energy bills, enhance your home’s comfort, and potentially increase your property value. These windows are available in many styles to suit various home types.
Learning about window energy efficiency ratings can help you choose windows suited for your climate. Compare different windows’ Energy Star and NFRC certifications and consult with professionals to find the best windows for your specific needs and budget.
FAQ About How Energy-Efficient Windows Work
What is low-e glass and how does it work?
Low-e glass is glass coated with a nontoxic coating that minimizes the amount of UV light that passes through it. By diminishing UV light, low-e glass can improve natural light while reducing cooling costs.
Are triple-pane windows worth the extra cost?
Whether triple-pane windows are worth the extra cost depends on whether you’re spending more on energy bills due to air escaping from your windows. Triple-pane windows consist of three layers of glass instead of the two that make up double-pane windows. While they help save energy, recouping the costs can take a long time. If you have many windows and plan to stay in your house long-term, triple-pane windows may be worth the cost.
How much energy can you save with energy-efficient windows?
You can save up to 13% on energy costs by replacing poorly performing windows with Energy Star-certified windows. How much you save depends on the window type you’re upgrading from and your local climate.
What is the best frame material for energy-efficient windows?
The best frame material for energy-efficient windows maximizes energy savings by offering insulative properties and a strong structure to support heavy windows. Wood, vinyl, and fiberglass are good frame materials for energy-efficient windows.
How long do energy-efficient windows last?
Energy-efficient windows can last for decades. Quality windows last an average of 15–30 years, but some last more than 50. However, the low-e coating on energy-efficient windows can lose effectiveness over time, diminishing energy savings.
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