Every window term, decoded.

An inert, harmless gas denser than air, sealed between the panes to slow heat transfer. A cheap, standard upgrade over a plain air gap.

DP rating

How much wind load a window is rated to withstand, tested to standards. A higher DP means it holds up to stronger storms.

Two panes of glass sealed with a gas gap between them — the NC standard for replacement windows.

EERO — emergency escape and rescue opening

A window big enough to climb out of in a fire (or for a firefighter to climb in). Bedrooms and finished basements generally require one.

The in-home worksheet a rep fills out to turn your current power bill into a projected monthly “savings” that helps justify the price.

A claim that you're buying straight from the maker with no middleman. Sometimes literally true; often a framing used to justify an in-home-sales premium.

pultruded fiberglass

A frame made of pultruded glass fibers — stronger and more dimensionally stable than vinyl, holding paint and shape in heat. A genuine step up, priced like one.

Andersen/Renewal by Andersen's proprietary composite frame material — a blend of wood fiber and PVC. A real material, marketed as a category of its own.

The layered, overlapping water barrier wrapped around a window opening that directs rain away from the wall. The difference between a dry wall and a hidden leak.

Haze or moisture trapped between the panes — a sign the sealed glass unit's seal has failed and its insulating gas has leaked out.

Two ways to replace a window. An insert (pocket) drops a new unit into your sound existing frame. A full-frame tear-out goes back to the rough opening and rebuilds it.

insulated glass unit

The sealed sandwich of two (or three) panes with a gas-filled gap and a spacer around the edge. The “glass” in a modern window is really this whole unit.

Two panes bonded to a tough plastic interlayer, so the glass holds together when broken. The basis of impact-rated coastal windows and a strong sound blocker.

A warranty term that means three very different things depending on whose lifetime — and the difference is almost never on the price sheet.

low-emissivity coating

A microscopically thin metallic layer baked onto window glass that lets daylight through but reflects heat. It's the single biggest driver of how a window performs.

MSRP, in a window pitch

A high “list” number a window is almost never actually sold at — the starting point a big discount is measured down from.

National Fenestration Rating Council label

The standardized white sticker on a new window listing its independently-tested U-factor, SHGC, and more — so you can compare any two windows on the same terms.

A quote's total divided by its window count — the only number that compares apples-to-apples across bids.

solar heat gain coefficient

How much of the sun's heat the window lets in, 0–1. Lower blocks more heat. In cooling-dominated North Carolina, this is the number you feel.

How well a whole window keeps heat in — the rate it loses heat. Lower is better; most quality NC windows land around 0.25–0.30.

UI — width plus height

A window's width plus its height in inches. Price books are banded by UI, so crossing a band bumps the same window into the next price bracket.

polyvinyl chloride

The most common replacement-window frame material — rigid PVC plastic. The NC value default, and itself split into tiers (recycled-content vs first-generation).

visible transmittance

How much visible light the window lets through, 0–1. Higher means a brighter room. Separate from how much heat it blocks.

The strip around the edge of the sealed glass unit that holds the panes apart. “Warm-edge” means it's made of a low-conducting material instead of plain aluminum.

Small drainage slots along the bottom outside edge of a window that let rainwater escape instead of pooling in the frame.