Window & Door Terms Explained: A Homeowner Glossary for Upstate South Carolina
Understanding window and door vocabulary should not feel confusing. This homeowner-friendly glossary explains common terms you may see in quotes, product brochures, NFRC labels, and replacement window recommendations so you can compare products with more confidence.
Use the A–Z links below to jump to a term, or scroll through the glossary to better understand window styles, glass options, energy ratings, and installation vocabulary.
Why These Terms Matter
When you understand common window and door terminology, it becomes much easier to compare quotes, ask better questions, and choose products that match your home, budget, and performance goals. Knowing what terms like U-Factor, Low-E, Air Leakage, and SHGC actually mean can help you avoid confusion and make a more informed decision.
Most Important Terms to Know Before You Buy
If you only remember a few terms, focus on these first:
Note: Performance ratings, glass options, and available features can vary by manufacturer, product line, and configuration.
A
Air Infiltration (Air Leakage)
The amount of air leaking in and out of a building through cracks in walls, windows, and doors.
Air Leakage
A measure of the rate of air leakage around a window or door in the presence of a specific pressure difference. The lower a window's air leakage rating, the better its airtightness.
Argon Gas
An inert, colorless, nontoxic gas used in insulating glass units to reduce heat transfer.
Awning Window
A window in which the sash is hinged at the top and opens by pivoting outward from the bottom using a crank handle.
B
Balance
A mechanism used in single and double hung windows as a means of counterbalancing the weight of the sash during opening and closing.
Bay Window
Traditionally made from three units with one large picture window flanked by two operating windows. The most popular combinations consist of double hung or casement style flanking windows.
Bottom Rail
The bottom horizontal part of a window sash.
Bow Window
Traditionally made of four or more windows joined together to form a delicate arch.
C
Cable Support Kit
A hardware set designed to anchor a bay or bow window to a structure.
Call Size (Catalog Size)
A manufacturer's reference number used to identify window and door dimensions.
Casement Window
A casement window is hinged on either side so the sash opens outward in a swinging motion to provide maximum ventilation.
Condensation
A deposit of water vapor which occurs when excess humidity in warmer air is released as water droplets onto a colder surface.
Conduction
Heat transfer through a solid material, where heat flows from a higher-temperature area to a lower-temperature area.
Cottage Window
A double-hung or single-hung window with an unequal top and bottom sash where the bottom sash is greater in height than the upper sash.
Crank Handle
Used in casement or awning windows, this handle has an arm and knob assembly.
D
Design Pressure (DP) Rating
A method of specifying window performance which measures a product's ability to withstand air and water forces while the window or door remains closed and locked.
Divided Light (Divided Lite)
A window opening with a number of smaller panes of glass separated and held in place by a grid system.
Double Glazing
Two pieces of glass separated by an air space to improve insulation against heat transfer.
Double Hung Window
A window consisting of two sashes operating in a master frame where both the upper and lower halves slide vertically and both tilt in for cleaning.
E
Egress Hardware
Type of hinge used in casement windows which allows for a wider opening to meet emergency exit requirements.
Egress Opening
The clear opening available for emergency escape or rescue through a window.
Energy Star
A program backed by the U.S. Environmental Protection Agency that helps identify energy-efficient products.
Extrusion
The process of producing vinyl or aluminum shapes by forcing heated material through a die.
F
Factory Mulled
Two or more window units attached together at the manufacturing facility.
Fenestration
The placement of window and door openings in a structure wall.
Fixed Panel
The non-operating panel of a slider window or sliding door.
Folding Crank Handle
Hardware with an arm and knob assembly where the handle folds down when not used.
Fusion Welding
The process of joining vinyl window or door frames and/or sashes by heating and bonding them together.
G
Garden Window
A box-shaped window with a slanted glass roof which projects from the side of a structure.
Glazing
The glass panes in a window, door, or skylight.
Glazing Bead
Pieces of molding around the inside of a window sash or frame which hold the glass unit in place.
Grids
Decorative grids that divide a glass unit into smaller openings to create multiple lites.
Grids Between the Glass (GBG)
A window or door option where grids are placed between panes of insulating glass.
H
Half Screen
A type of screen which covers only one half of the window.
Header (Head)
The upper horizontal part of a window frame.
Heat Gain
Transfer of heat from the outside to the inside of a structure.
Heat Loss
Transfer of heat from the inside of a structure to the outside.
Hopper Window
A window where the sash is hinged at the bottom and pulls inward for opening.
Horizontal Slider (Slider)
A window where one or both panels slide horizontally past each other.
I
ICC (International Code Council)
A national organization which publishes model building and energy codes.
Infiltration
See Air Leakage.
Insulation Glass Unit
Two or more panes of glass spaced equally apart and hermetically sealed, forming a single glazed unit.
Integral Nailing Fin
Part of the master frame of a new construction window used to aid installation and strength.
Interlock
An overlap between window or door components that reduces air infiltration and increases security.
J
J-Channel
An optional extrusion part on a new construction frame that allows siding to slip between the trim and nailing fin.
Jamb
The vertical part at either side of a window frame.
Jamb Extension
Material attached to the inside edges of the window or door to extend its width and adapt it to a thicker wall.
K
Keeper
A bracket used as a latching point in locking hardware.
Knocked-Down
Describing the final product as unassembled, most commonly a patio door.
Krypton Gas
An inert gas used in insulating windows to reduce heat transfer. Less common and more expensive than argon.
L
Laminated Glass
Two or more panes of glass bonded together with a layer of plastic in between.
Lift Rail
The bottom part of the sash on a double or single hung window designed for lifting the operating sash.
Light (Lite)
When glass is divided by a grid into multiple smaller openings, those openings are called lites.
Lintel
A horizontal beam above a window or door opening which supports the weight of the wall above it.
Low-Emittance Coating (Low-E)
Microscopically thin coatings applied to glass to help block UV rays and infrared heat.
M
Mechanical Window
A window in which the corners are assembled using screws instead of welded corner construction.
Meeting Rail
The part of a window or sliding door where two panels meet.
Mullion
A part used to structurally join two or more window or door units.
Mulled Unit
Two or more window or door units joined together.
Multipoint Locking System
A locking system with more than one locking point.
N
Nailing Fin (Nailing Flange)
An integral part of a new construction window or patio door frame through which nails are driven to secure the frame.
National Fenestration Rating Council (NFRC)
The organization that provides standardized performance ratings for windows and doors, including U-Factor, SHGC, and Visible Transmittance.
O
Obscure Glass
Any textured glass, usually frosted, used for privacy while still allowing light in.
Operable Window
Any type of window which can be opened for ventilation.
Operator
Crank-operated hardware used in opening and closing casement windows.
Oriel Window
A double or single hung window with an unequal top and bottom sash where the top sash is greater in height than the lower sash.
P
Pane
A single sheet of glass.
Panel
The component of a sliding glass door consisting of a glass unit in a frame.
Picture Window
A fixed window which does not open for ventilation.
R
R-Value
A measure of the resistance to heat flow. A higher R-Value means greater insulating value.
Rail
The horizontal part of a window sash.
Retrofitting
Adding or replacing items on existing structures.
Rough Opening
The opening in a wall into which a door or window is installed.
S
Sash
The part of a window which includes the glass unit and the frame sections directly attached to it.
Screen
Mesh stretched over a frame which allows air to pass through while stopping insects.
Seal Failure
Loss of the airtight seal in the insulated glass unit which results in fogging between the glass panes.
Seat Board
A board cut to fit the contour of a bay or bow window which provides a seat or shelf space.
Sill
The lowest horizontal part of a window or door frame.
Simulated Divided Lights (SDL)
A window or door unit with grilles placed between and on the glass surface to create the appearance of smaller panes.
Single Glazing
A single pane of glass in a window or door.
Single Hung Window
A window consisting of two sashes where the upper sash is fixed and the bottom sash moves up and down.
Single-Strength Glass
Glass with a thickness between 0.085" and 0.100".
Skylight
A roof window which gives light and, if operable, ventilation.
Slider Window
A window consisting of two or more sashes which operate by sliding horizontally past each other.
Sliding Glass Door (Patio Door)
A door consisting of two or more panels which move horizontally on a track.
Solar Heat Gain Coefficient (SHGC)
A measurement of how much solar heat passes through a window. The lower the SHGC, the less solar heat enters the home.
Spacer
A material which separates the panes of glass to create the airspace in an insulating glass unit.
Stress Crack
A defect resulting from a stress condition originating at a point along the edge of a piece of glass.
T
Tempered Glass
Glass strengthened by reheating and suddenly cooling it so it breaks into small pieces when shattered.
Thermal Break
A barrier between elements of high conductance which reduces the flow of heat.
Thermal Expansion
A dimensional change in a material due to temperature changes.
Tilt Latch
A mechanism at the top of each sash which allows inward movement for cleaning and removal.
Tinted Glass
Glass colored in the manufacturing process by the addition of a mineral admixture.
Transom
A window above a door or another window, usually non-operable.
Triple Glazing
Three pieces of glass separated by two air spaces to improve insulation against heat transfer.
True Divided Lite
A window opening comprised of multiple individual smaller panes of glass separated by grilles.
U
U-Factor
A measurement of how much heat passes through a window or door. The lower the U-Factor, the better the insulating performance.
V
V-Groove
A decorative pattern grooved into the glass using a special process.
Veneer
A thin sheet or layer of wood.
Virgin Extrusion
Extrusions produced from virgin vinyl with no regrind added.
Visible Transmittance (VT)
The percentage of available light which comes through a window. The higher the VT, the more daylight comes in.
W
Warm-Edge Technology
Use of low-conductance spacer materials to reduce heat transfer near the edges of insulated glass units.
Warping
What happens when an object is twisted out of shape.
Weather Stripping
Material which covers the joints between the sashes and master frame, reducing air and water infiltration.
Weep Hole
A small opening in a window or door sill through which water may drain to the building exterior.
Frequently Asked Questions
Which window terms matter most when comparing quotes?
For most homeowners, the most important terms are U-Factor, SHGC, Low-E glass, Air Leakage, and NFRC ratings. These help you compare comfort, efficiency, and performance more accurately.
What does NFRC mean on a window label?
NFRC stands for National Fenestration Rating Council. It provides standardized performance ratings for windows and doors so homeowners can compare products more clearly.
What is a good U-Factor for replacement windows?
In general, a lower U-Factor means better insulating performance. The right number depends on the product, glass package, and climate zone.
What does SHGC mean on a window label?
SHGC stands for Solar Heat Gain Coefficient. It measures how much solar heat passes through the window. Lower SHGC usually means less heat enters the home.
What is Low-E glass?
Low-E glass has a microscopically thin coating designed to help reflect heat and block harmful UV rays while still allowing natural light into the home.
What is the difference between single hung and double hung windows?
A single hung window usually has a fixed upper sash and a movable lower sash. A double hung window has two operable sashes, which can improve ventilation and make cleaning easier.
Need Help Comparing Window or Door Options?
Now that you understand the most common window and door terms, you’ll be in a better position to compare quotes, ask the right questions, and choose products that truly fit your home. If you’re considering replacement windows in Upstate South Carolina or new window and door services, Yan Windows is here to help with honest guidance, quality products, and no-pressure estimates.
