• Air Chambers – Small honeycomb spaces within the sash and frame which help to insulate and strengthen the window.
• Air Infiltration – The amount of air that passes between a window sash and frame. In windows it is measured in terms of cubic feet or air per minute, per square foot of area. The lower the number, the less air the window lets pass through.
• Awning Window – A top-hinged window that swings outward for ventilation.
• Bay Window – An angled combination of three windows that project out from the wall of the home. The windows are commonly joined at 30- or 45-degree angles.
• Bow Window – An angled combination of windows in 3-, 4- or 5-lite configurations. The windows are attached at 10-degree angles to project a more circular, arced appearance.
• Cam Lock and Keeper – The mechanisms which pull the sash together when placed in the locked position.
• Casement Window – A window with a side-hinged sash that opens outward for ventilation.
• Condensation – The formation of moisture on the surface of the window.
• Conduction – Heat loss in windows that occurs primarily through the edges of the glazing and through the sash and frames.
• Convection – Heat loss that occurs due to air movement between the glazings of a window.
• Dead-air space – The space between the panes of glass of an I.G. Unit.
• Desiccant – A material used in insulating glass to absorb water vapor which causes fogging.
• Double Hung Window – A window that has two operable sash which slide vertically.
• Drainage Holes – Small openings designed to allow water to escape that might otherwise accumulate in a window’s sill.
• ENERGY STAR® – ENERGY STAR® is an independent government program establishing a standard set of guidelines to recognize the energy efficiency of various products. ENERGY STAR® guidelines are used in conjunction with a variety of building materials, including windows and patio doors. Over the past ten years, ENERGY STAR® guidelines have helped double the efficiency of windows they endorse.
• Glazing – The process of sealing the glass to the sash.
• I.G. Unit (Insulating Glass Unit) – Two or more lites of glass separated by a spacer and hermetically sealed at the glass edges.
• Lite – A unit of glass in a window.
• Obscure Glass – Glass that has been made translucent instead of transparent.
• Picture Window – A window that has no moveable sash.
• Sash – The part of the window which contains the glass.
• Sill – The horizontal, bottom section of the main frame.
• Sill Extension – An extrusion that is attached to the bottom of the window to cover the gap between the sill and the rough opening.
• Slider Window – A window in which the sash move horizontally. Sliders are available in a 2- or 3-lite configuration, with the 3-lite having operable end vents.
• Solar Heat Gain – The percentage of heat gained from both direct sunlight and absorbed heat. The smaller the number, the greater the ability to reduce solar heat gain.
• Spacer – Material placed between two or more pieces of glass in order to maintain a uniform width between the glass, and prevent sealant distortion.
• Sweep Sill – A flexible fin usually made of rubber or polypropylene which is fastened to either the movable sash or the stationary frame and sweeps against the opposing component to form a barrier.
• Tempered Glass – Glass when broken, it breaks into pebbles instead of shards.
• Thermal Break – An insulating material applied to a high conducting material to slow the transfer of heat.
• Tilt Latch – Mechanism that unlocks the sash and allows it to tilt in from the main frame.
• U-value – Amount of heat transferred through a material. The lower the U-value, the slower the rate of heat flow and the better the insulating quality. U-values are the reciprocal of R-values. (U-value of 0.25 is equal to R-value of 4)
• Warm Edge Spacer – Spacers made from insulating material such as foam, butyl, thermo-plastic, or thermally improved metals and therefore conduct significantly less heat energy than standard spacers.
• Water Leakage – The penetration of water that would continuously or repeatedly wet parts of a building or components not designed to be wetted.
• Weather-stripping – Material used to form a weather-resistant seal around operable sash

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