Glossary of Window Terms

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.

Argon Gas - An odorless, colorless, tasteless, non-toxic gas which is six times denser than air. It is used to replace air between the glass panes to reduce temperature transfer.

Awning Window - A top-hinged window that swings outward for ventilation.

Balance System - Device for holding vertically sliding sash in any desired position through the use of a spring or weight to counterbalance the weight of the sash.

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.

Casement Window - A window with a side-hinged sash that opens outward for ventilation.

Condensation Resistance Factor - A measure of the effectiveness of a window or glazing system to reduce the potential for condensation. The higher the condensation resistance factor, the more efficient the window and glazing system.

Convection - Heat transfer by currents that flow from a warm surface to a colder one.

Double Hung Window - A window that has two operable sash which slide vertically.

Double-strength Glass - Glass with a thickness of approximately 1/8".

ENERGY STAR® - ENERGY STAR® is an independent U.S. 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.

Grids - Decorative horizontal or vertical bars installed between the glass panes to create the appearance of the sash being dividing into smaller lites of glass.

Head - The horizontal top portion of the main frame.

I.G. Unit (Insulating Glass Unit) - Two or more lites of glass separated by a spacer and hermetically sealed at the glass edges.

Jamb - Vertical sections of the main frame.

Krypton Gas - An inert, odorless, colorless, tasteless, non-toxic gas which is about 12 times denser than air. It is used to replace air between the glass panes to reduce temperature transfer and deter convection. Used when a higher performance is desired than that produced with Argon gas.

Lift Handle - A handhold for raising and lowering the sash. Handle implies that the handhold is not continuous across the sash.

Lift Rail - A handhold for raising and lowering the sash. Rail implies that the handhold is continuous across the sash.

Lite - A unit of glass in a window.

Low E (Emissivity) Glass - Glass with a transparent metallic oxide coating applied onto or into a glass surface. The coating allows short-wave energy to pass through but reflects long-wave infrared energy which improves the U-value.

Main Frame - The head, sill and jambs sections of a window.

Mullion - A vertical or horizontal connecting unit between two or more windows.

Obscure Glass - Glass that has been made translucent instead of transparent.

Patio door - A glass door that slides open and close on adjustable tandem rollers. Available in 2- or 3-lite configurations with the operable panel available in any position.

Picture Window - A window that has no moveable sash.

R-value - Resistance a material has to heat flow. The higher the R-value, the greater the resistance, the better the insulation. R-values are the reciprocal of U-values (R-value of 4 is equal to U-value of 0.25)

Radiation - Wave energy transmitted directly from one object to another through the atmosphere or through transparent or translucent materials. The energy radiated is either transmitted, absorbed, reflected or a combination of all three.

Sash - The part of the window which contains the glass.

Shading Coefficient - The ratio of solar heat that is transferred through a glazing material relative to the solar heat transferred through 1/8" clear glass. The lower the number the more efficient the window is at reducing solar heat gains.

Sill - The horizontal, bottom section of the main frame.

Single-strength Glass - Glass with a thickness of approximately 3/32".

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.

Stile - The vertical sections of the sash.

Tempered Glass - Glass with a surface compression of not less than 10,000 psi, or an edge compression of not less than 9,700 psi. When broken, the glass breaks into pebbles instead of shards.

Tilt Latch - Mechanism that unlocks the sash and allows it to tilt in from the main frame.

Total Unit U- and R-values - The U- and R-values of the window calculated from the average U and R-values from the center of glass, edge of glass, and 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)