Glossary

The terms in our tables, defined once. Hover or tap a dotted term anywhere on the site to see the same definition.

Air infiltration: Air that leaks through a closed window under test pressure, in cubic feet per minute per square foot. Lower is tighter.
Approval number: The ID of a state or local product approval, such as a Florida Product Approval or Miami-Dade NOA. Building officials check it at permit.
BIM / CAD: Drawing and model files (Revit, DWG) architects can place in their plans.
Climate zone: The IECC zone, 1 (hot) to 8 (very cold), assigned by county. Each zone has its own window limits.
CSI section: The MasterFormat section architects file the product under in a specification, e.g. 08 52 00 for wood windows.
Design pressure: The wind load, in pounds per square foot, a window is rated to resist. Upper floors, corners and coastal sites need more.
Frame: The frame material. Aluminum-clad wood has a timber frame with an aluminum skin outside; all-wood shows timber on both faces.
Frame depth: How thick the frame is from inside to outside. Deeper frames hold thicker glass and usually insulate better.
Glass seal warranty: Coverage against the sealed glass unit losing its seal, which shows as fogging between the panes.
Glass stress crack: Coverage for glass that cracks on its own from thermal stress, not from impact.
Glazing: The number of glass panes in the sealed unit: double, triple or quad. More panes insulate better and weigh more.
Impact rated: Tested to withstand wind-borne debris (ASTM E1886/E1996). Required in hurricane debris regions unless shutters are used.
Installation type: How the unit attaches to the opening: nail fin, flush fin, block frame or replacement insert.Nail fin suits new construction; inserts suit replacement without removing trim; block frames are fixed with straps or screws.
Lead time: Typical weeks from a confirmed order to delivery. Custom wood and clad lines usually take longest.
Low-e: A thin metal-oxide coating on the glass that reflects heat. Different coatings trade solar gain against daylight.
Max sash weight: The heaviest opening sash or sliding panel the hardware is rated to carry. Limits size with heavy triple glass.
Max tested size: The largest unit the manufacturer tested at its rating. Bigger units may need engineering or a lower rating.
NAFS rating: Performance class and grade under the North American Fenestration Standard, e.g. CW-PG70. Shows the loads the window passed in testing.The class (R, LC, CW, AW) sets the test size and severity. The grade (PG) is the design pressure tested, in psf.
NFRC: National Fenestration Rating Council: the US program that certifies whole-window U-factor, SHGC and VT for energy codes.
OITC: Outdoor-indoor transmission class: like STC but weighted for low traffic and aircraft noise.
Operation: How the window opens: casement, awning, hung, sliding, tilt-turn or fixed. The symbols show the hinge side or travel direction.
Performance class: NAFS class, from lightest to toughest: R (residential), LC (light commercial), CW (commercial), AW (architectural).
PHI certified: Certified by the Passive House Institute as a component for very low-energy buildings in a stated climate.
Prescriptive limit: The maximum U-factor or SHGC the energy code allows when you follow its simple checklist path.
Price tier: RFV’s relative price band, from $ to $$$$, comparing installed cost per opening within residential windows.
Rating: The NAFS performance class and grade, e.g. CW-PG70. Shows the loads the window passed in testing.
SHGC: Solar heat gain coefficient: the share of the sun’s heat that gets through, from 0 to 1. Lower keeps homes cooler.Warm climates cap SHGC in the energy code. In cold climates a higher SHGC on south walls can help heating.
STC: Sound transmission class: how well the window blocks speech-range noise. Higher is quieter; 32 and up is noticeably quiet.
Thermal break: An insulating strip separating the inside and outside of an aluminum frame. Without one, aluminum cannot meet most energy codes.
Transferable: Whether the warranty passes to the next owner if the home is sold.
U-factor: How fast heat passes through the whole window. Lower is better insulation. US values are in Btu/h·ft²·°F.Energy codes use the NFRC-rated whole-window value, which includes the frame, not just the glass.
Ug (centre of glass): U-value of the glass alone, measured at its centre. The whole window, including the frame, performs worse.
Uw (PHI): Whole-window U-value from the Passive House Institute, at its reference size. Not an NFRC rating, so it does not show code compliance.
VT: Visible transmittance: the share of daylight that gets through, from 0 to 1. Higher means brighter rooms.
Water test pressure: The wind pressure at which the window kept water out in testing. Higher resists wind-driven rain better.