What Makes an Energy Star Window?
Windows provide our homes with warmth, light and ventilation, but age, type, overall condition and a lack of maintenance can also seriously impact a home’s energy efficiency. If your home has very old or inefficient windows, it can be cost-effective to replace them with windows that have earned an ENERGY STAR® efficiency rating. Choosing and installing an ENERGY STAR window can help minimize your heating and cooling costs.
What is an ENERGY STAR® Label?
The ENERGY STAR® label was established to reduce greenhouse gas emissions and other airborne pollutants caused by inefficient energy use while making it easier for consumers to identify such products. Windows and other residential products earn an ENERGY STAR® label by meeting strict efficiency requirements in ENERGY STAR® product specifications.
All new windows are independently tested and certified by the National Fenestration Rating Council (NFRC). The Environmental Protection Agency (EPA) establishes these specifications based on the following set of principles:
- Product categories must contribute significant energy savings nationwide. All products are rated based on performance in four basic U.S. climate zones: Northern, North-Central, South-Central and Southern.
- In addition to offering increased energy efficiency, qualified products must deliver the features and performance they offer to consumers.
- If a qualified product is more expensive than a conventional, less-efficient counterpart, consumers will recover their investment (in reduced utility bills) through increased energy efficiency, within a reasonable time of installation.
- Energy efficiency can be achieved through broadly available, non-proprietary technologies offered by more than one manufacturer.
- A product’s energy consumption and performance can be measured and verified via testing.
- Labeling would effectively differentiate products and be visible for purchasers.
The ENERGY STAR® Testing Process for Windows
ENERGY STAR bases its qualifications only on U-factor and solar heat gain coefficient ratings, which are described below.
Different types of windows prevent or allow varying degrees of heat gain and loss due to the following conditions:
- Direct conduction through the glass or glazing and the window frame
- The amount of heat filtered into a home (usually from direct sunlight) and the amount of heat lost from within a home
- The levels of air leakage through and around windows
These properties are measured and rated according to the following energy performance characteristics before earning an ENERGY STAR rating label:
U-factor: A window conducts non-solar heat flow, or heat only from the outside temperature at this rate. A window’s U-factor may refer to just the glass or glazing, not the performance of the entire window, including spacer material and framing. The lower a window’s U-factor – the more energy-efficient the window.
Solar heat gain coefficient (SHGC): The measurement accounts for a fraction of the solar radiation that is either directly transmitted or absorbed through a window and released as heat inside your home. The lower the SHGC, the less solar heat it transmits and the greater it’s shading ability.
- Windows with a high SHGC rating are more effective at collecting solar heat during the winter.
- Windows with a low SHGC rating help reduce cooling loads during the summer by blocking solar heat gain.
The climate in which you live, each window’s level of external shading and directional orientation help determine the optimal SHGC for every window in your home.
Air leakage: This is the rate of air movement directly around a window. A window with low air leakage is naturally tighter than one with a high air leakage rating.
The ability of glazing in a window, door, or skylight to transmit sunlight into a home can be measured and rated according to the following energy performance characteristics:
Visible transmittance (VT): This is an optical measurement indicating the fraction of visible light transmitted through a window. This is separate from the SHGC rating, since many modern windows include tinted or coated glazings that allow differing amounts of visible, infrared and ultraviolet light. The VT you need for your home’s windows should be determined by how much natural light enters your home and if interior glare should be reduced in a particular space.
Light-to-solar gain (LSG): The ratio between the SHGC and VT measurements, which provides a gauge of the relative efficiency of different glass or glazing types in blocking heat gains without interfering with the amount of daylight entering your home. The higher the number, the more light is transmitted without adding excessive heat. However, this energy performance rating isn’t always provided.
What Makes a Window Energy Efficient?
Several points are considered when rating windows as being energy efficient. Here is a list of the key features all windows are rated on:
- Quality frame materials: Because there are a variety of durable, low-maintenance framing materials that reduce heat transfer while providing good insulation, each is judged according to its own benefits.
- Multiple panes: Two panes of glass, with an air- or gas-filled space in the middle, insulate much better than a single pane of glass. Some ENERGY STAR-qualified windows include three or more panes for even greater energy efficiency. Multiple-paned windows also increase impact resistance and sound insulation.
- Low-E glass: Low emissivity (Low-E) glass coatings reflect infrared light, keeping heat inside in winter and outside in summer. They also reflect damaging ultraviolet light, which helps protect interior furnishings, rugs and paintings from fading.
- Gas fills: Some energy-efficient windows contain argon, krypton or other gasses between the panes. These gases are odorless, colorless and non-toxic – and provide far better insulation than regular air.
- Warm edge spacers: Heat gain and loss through windows often occurs through the outer edges https://www.cialissansordonnancefr24.com/acheter-cialis/ of window panes. Non-metallic and metal/nonmetal hybrid spacers insulate pane edges, reducing heat transfer through the window. A spacer also keeps a window’s glass panes the correct distance apart.
Window Framing Materials
ENERGY STAR-certified windows come in a variety of framing materials, all of which are rigorously tested for their specific energy efficiency.
- Fiberglass frames are strong, durable, low maintenance and provide good insulation. Fiberglass frames can be either hollow or filled with foam insulation.
- Vinyl frames are low maintenance and provide good thermal insulation. Sections may be hollow or filled with foam insulation. Wide vinyl sills may be reinforced with metal or wood.
- Aluminum frames are durable, low maintenance, recyclable, and typically have at least 15% recycled content. Frame design typically includes thermal breaks to reduce conductive heat loss through the metal.
- Wood frames are strong, provide good insulation, and are generally favored in historical neighborhoods. The exterior surfaces of many wood windows are clad (or covered) with aluminum or vinyl to reduce maintenance.
- Combination frames use different materials separately throughout the frame and sash to provide optimal performance. For example, the exterior side of a frame could be vinyl while the interior side could be wood.
- Composite frames are made of various materials that have been blended together through manufacturing processes to create durable, low maintenance, well-insulated windows.
You’ll find many options to consider when selecting the type and style of windows to use in your home, but doing a little research on every window’s ENERGY STAR energy performance rating first will benefit your family, your home and your wallet in the long run.