If you find yourself considering the replacement of doors, windows or skylights here is some useful information from the energy.gov website about how energy performance is rated.
You can use the energy performance ratings of windows, doors, and skylights to tell you their potential for gaining and losing heat, as well as transmitting sunlight into your home.
Performance Testing, Certification, & Labeling
The National Fenestration Rating Council (NFRC) operates a voluntary program that tests, certifies, and labels windows, doors, and skylights based on their energy performance ratings. The NFRC label provides a reliable way to determine a window’s energy properties and to compare products.
The NFRC label can be found on all ENERGY STAR® qualified window, door, and skylight products, but ENERGY STAR bases its qualification only on U-factor and solar heat gain coefficient ratings, which are described below.
Energy properties are measured and rated according to these energy performance characteristics:
- U-factor is the rate at which a window, door, or skylight transmits non-solar heat from outside to inside. It is expressed in units of Btu/hr-ft2-oF. For windows, skylights, and glass doors, a U-factor refers to just the glass or glazing and not the frame. NFRC U-factor ratings represent the entire window and frame performance. A lower U-factor, means a more energy-efficient window, door, or skylight.
- Solar heat gain coefficient (SHGC) is the percentage of solar radiation passed through a window, door, or skylight — either passed directly and/or absorbed and released as heat inside a home. A lower SHGC means less solar heat is transmitted, and the greater the light-blocking ability. A product with a high SHGC rating is more effective at collecting solar heat during the winter. A product with a low SHGC rating is more effective at reducing cooling loads during the summer. Your home’s climate, orientation, and external shading will determine the optimal SHGC for a particular window, door, or skylight.
- Air leakage rate is the rate of air movement around a window, door, or skylight when air pressure is higher on one side than the other. We express Air leakage rate in units of cubic feet per minute per square foot of frame area (cfm/ft2). A product with a low air leakage rating is tighter than one with a high air leakage rating. Note that proper installation greatly affects air leakage.
Sunlight Transmittance
The degree to which the glazing in a window, door, or skylight transmits sunlight into a home can be measured and rated according to the following energy performance characteristics:
- Visible transmittance (VT) is the percentage of the visible spectrum of sunlight (380 to 720 nanometers), weighted by the sensitivity of the human eye, being transmitted through the glazing of a door, window, or skylight. A higher VT value means moret visible light. VT is transmitted. The value is expressed as a number between 0 and 1. The VT you need for a door, window, or skylight can be determined by your home’s daylighting requirements and/or whether you need to reduce interior glare in a space.
- Light-to-solar gain (LSG)is the ratio between the SHGC and VT. It provides a gauge of the relative efficiency of different glass or glazing types in transmitting daylight while blocking heat gains. The higher the number, the more light is transmitted without adding heat. This energy performance rating isn’t always provided.
Review the state fact sheets or use the window selection tool for new construction or existing homes from the Efficient Windows Collaborative to determine the desired performance ratings for your climate.
Vero Beach Window Cleaners shares this information to help you make informed future decisions about the windows, doors, and skylights in your home or office. In the meantime, why not let the expert window cleaners at Vero Beach Window Cleaners give you a new outlook on like by professionally cleaning the windows in your home or office.
Call us today at (772) 281-7759.
