Glossary

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Edge effects
Two-dimensional heat transfer at the edge of a glazing unit due to the thermal properties of spacers and sealants.
Electrochromics
Glazing with optical properties that can be varied continuously from clear to dark with a low-voltage signal. Ions are reversibly injected or removed from an electrochromic material, causing the optical density to change.
Electromagnetic spectrum
Radiant energy over a broad range of wavelengths.
Emergency exit window
Fire escape window (egress window) large enough for a person to climb out. In U.S. building codes, each bedroom must be provided with an exit window. The exact width, area, and height from the floor are specified in the building codes.
Emittance
The ratio of the radiant flux emitted by a specimen to that emitted by a blackbody at the same temperature and under the same conditions.
Emissivity
The relative ability of a surface to reflect or emit heat by radiation. Emissivity factors range from 0.00 to 1.00. The lower the emissivity, the less heat that is emitted through a window system. Emissivity is typically measured by U-factor (or its inverse, R-factor).
ENERGY STAR® windows program
A voluntary partnership between the U.S. Department of Energy (DOE) and the fenestration industry to promote sales of energy-efficient windows, doors and skylights. The program establishes three climate regions with one recommended product designation for each region. All ENERGY STAR® windows must be NFRC-rated, certified and labeled for both U-factor and solar heat gain coefficient.
ENERGY STAR® label
A label that indicates a window meets ENERGY STAR® program energy-efficiency requirements for a specific region, and is at least 40% more efficient than products required under the most common national building codes.
Evacuated glazing
Insulating glazing composed of two glass layers, hermetically sealed at the edges, with a vacuum between to eliminate convection and conduction. A spacer system is needed to keep the panes from touching.
Exterior stop
The removable glazing bead that holds the glass or panel in place when it is on the exterior side of the light or panel, in contrast to an interior stop located on the interior side of the glass.
Extrusion
The process of producing vinyl or aluminum shapes by forcing heated material through an orifice in a die. Also, any item made by this process.
Eyebrow windows
Low, inward-opening windows with a bottom-hinged sash. These attic windows built into the top molding of the house are sometimes called "lie-on-your-stomach" or "slave" windows. Often found on Greek Revival and Italianate houses.