Energy-efficient homes can save homeowners and renters a significant amount of money on their utility bills. According to the U.S. Department of Energy’s (DoE) ENERGY STAR program, ENERGY STAR-certified homes and apartments are on average 20% more energy-efficient than new homes built to code. Energy-efficient homes can cut down your energy bills significantly.
Part of making your home more energy efficient is replacing your windows with energy-efficient high-performance windows. DoE data suggests that up to 30% of the energy used to heat and cool your home is needed to compensate for heat loss and heat gain through the windows. Energy-efficient windows are an important consideration to improve your home’s energy efficiency and at the same time the comfort of your home.
Replacement Windows Can Lower Your Utility Bills
Replacing your old windows affects your utility bills by considerably reducing your energy cost. According to ENERGY STAR, replacing existing single-pane windows with ENERGY STAR certified windows can save you somewhere between $101 and $583 a year. The actual utility bill savings vary based on your local climate conditions, utility rate and the characteristics of your home. If you already have double-pane windows, the savings from replacing them with ENERGY STAR certified windows range between $27 and $197.
DoE estimates suggest that replacing your windows with ENERGY STAR certified windows can reduce your energy bill by an average of 12% compared to non-certified new products and significantly more compared to your old windows. The national average varies considerably based on the climate in your area.
The type of window that’s right for your home varies with your local climate conditions. Gas-filled windows with low-E coatings help reduce heat loss, especially in colder climates whereas coated windows help reduce heat gain in warmer climates. In temperate climates with both hot and cold seasons, a window with good insulation and low solar heat gain increases your home’s energy efficiency.
Selecting a Replacement Window
The energy savings of replacing windows not only depend on the type of window you choose and features such as frame glazing, gas fillings, and windows operation, but also on your local climate conditions. To maximize your energy savings, you should replace your window frames as well.
While windows come with different designs to match the style of your home, they should as a minimum have an ENERGY STAR label. These windows typically exceed energy code requirements and include performance ratings from the National Fenestration Rating Council (NFRC). NFRC ratings help you determine the energy performance of the window and make it easy to compare different products. Use the NFRC label to select the best window for your climate zone.
NFRC Window Label
The NFRC window label shows the energy performance characteristics of the window and lists manufacturer and product information to help consumers select the right window. All products are rated in two standard sizes to make it easier to compare products. The window energy performance is measured in two categories.
The U-factor describes the rate of heat flow through the window or how well the window prevents heat from escaping. U-factor ratings typically fall between 0.15 for triple glazed windows and 1.20 for single glazed windows. A lower U-value means better thermal resistance or better insulation of the window which makes especially sense in colder climates.
The Solar Heat Gain Coefficient (SHGC) describes the amount of solar radiation admitted through the window and is expressed as a number ranging from 0 to 1. A lower SHGC means less heat gain through the window which is especially important in hot climates.
The NFRC label includes more parameters to provide additional information. Visible Transmittance (VT) describes how much visible light is transmitted through the window. A higher VT means more daylight is transmitted to naturally light your home. Air Leakage (AL) measures heat loss and heat gain by infiltration through cracks in the window assembly. A lower AL means less air can pass through the window. Some manufacturers also indicate the Condensation Resistance (CR), which measures the expected formation of condensation on the interior window surface. A higher CR rating means less condensation formation on the window.
How Energy Efficient Windows Work
Energy-efficient windows include several elements that increase their energy performance. The U-factor of the entire window assembly depends on the size of the window and its individual components.
To reduce heat loss in the winter, insulation is increased by adding more panes to the windows. Energy-efficient windows have at least two and often three glass panes. The space between the individual panes is filled with a noble gas like argon or krypton to further reduce heat transfer through the window.
Thin layers of metallic oxides are added to low-emissivity glass windows to reflect the sunlight and reduce heat gain in the summer. These layers also help reduce heat loss in the winter. Energy-efficient windows include vinyl or fiberglass frames with better insulation.
Alternative Ways to Improve Your Windows’ Energy Performance
Replacing your windows can lower the energy consumption of your home significantly. Depending on the overall condition of your home, windows may not be the biggest source of heat loss though. Air-sealing your home and improving its insulation are important to increase the overall energy efficiency of your home.
Replacement windows require significant investment and the return on investment varies with your local climate conditions, utility rates and the overall energy efficiency of your home. If replacing your old windows isn’t cost-effective, there are alternative solutions to improve the energy efficiency of your existing windows.
Besides sealing air leaks with caulking and weather-stripping, you can improve your window insulation by adding treatments and coverings to the glass itself, such as solar control films or layers of plastic. You can add storm windows or shutters to improve insulation or exterior shading to reduce heat gain.
Replacement Windows Have More Benefits
Energy-efficient windows reduce noise pollution from the street and windows with low-E coatings reduce damage from the sun’s UV light inside your house. Better insulation keeps the interior glass warmer, increasing comfort in your home. New windows also increase the value of your home.
Some states, cities, and utilities offer rebates or incentives to increase home energy efficiency to include replacement windows. If you replace your windows with ENERGY STAR-certified products you may also benefit from a federal tax credit.