Window Terms Glossary: Read Your Quote Like a Pro

The label: U-factor, SHGC, and air leakage

NFRC label. The sticker from the National Fenestration Rating Council, certifying performance numbers measured the same way for every manufacturer. It’s the one apples-to-apples comparison in the industry, and it rates the whole window — glass, frame, and spacer together — not just the glass.

U-factor. How much heat passes through the window. Lower is better, and under 0.30 is a solid target for Pennsylvania. Ask for the number on the exact product and glass package you’re being quoted, not the brochure’s best case.

SHGC, or solar heat gain coefficient. How much of the sun’s heat comes through, on a scale of 0 to 1. Lower keeps summer heat out; higher lets in free winter warmth.

Air leakage rating. How much air passes through the assembly. Lower is better, and it’s the number nobody mentions even though drafts are why most people call in the first place.

R-value vs U-factor. R-value measures resistance to heat flow, so higher is better — the scale you know from insulation. U-factor is roughly its inverse, and it’s what windows are rated with. Never compare an R-value claim against a U-factor number.

The glass package: Low-E, IGU, argon, spacers

IGU, or insulated glass unit. The sealed sandwich of two or three panes with a spacer around the edge and dry air or gas between them. When someone says a seal failed or a window fogged, this is the part they mean.

Low-E. A microscopically thin, essentially invisible metallic coating on the glass that reflects heat back where you want it — indoors in winter, outdoors in summer. Coatings are tuned for different climates; ours calls for one suited to cold winters and humid summers.

Argon and krypton. Inert gases used instead of air between panes because they conduct less heat. Argon is the standard fill. Krypton performs slightly better in narrow gaps and costs more.

Spacer. The strip that holds the panes apart around the edge of the unit. Its material matters more than it sounds like it should.

Warm-edge spacer. A spacer made of low-conducting material rather than plain aluminum, which reduces the cold bridge at the edge of the glass. It cuts condensation along the bottom of the pane and helps the seal last, because the assembly moves less.

Laminated glass. Two panes bonded to a plastic interlayer: the quiet, secure option.

Anatomy: sash, jamb, sill, brickmold

Sash. The moving frame that holds the glass. A double-hung window has an upper and a lower sash; a picture window’s glass is fixed and has no operating sash.

Jamb. The vertical sides of the window frame — the surfaces the sashes run against.

Sill. The bottom of the window frame, sloped outward to shed water. Its corners are where rot starts, and where you or an inspector should press for soft wood.

Brickmold. The exterior trim where the window meets the wall, brick or not. Keeping or replicating brickmold is often how a replacement window keeps an older Pennsylvania home looking right.

Muntin and grille. Muntins are the true dividers between individual panes in a divided-light window. Grilles imitate that look on a single sealed unit — between the panes, applied to the surface, or both. Nearly every quote you’ll read means grilles.

Weep hole. Small drainage openings at the bottom of the frame or exterior sill that let water escape. They must stay clear; painting or caulking them shut traps water inside the frame.

How it opens

Double-hung. Two sashes that slide vertically. Tilt-in sashes pivot inward so you can wash both sides from indoors — the feature forever-home owners appreciate most once they’ve lived with it.

Single-hung. Same look, but only the bottom sash moves.

Casement. Hinged at the side and cranked open like a door. It seals tightly because the sash presses against the frame when latched, and it catches side breezes well.

Awning. Hinged at the top and opening outward at the bottom, so it can stay open in light rain. Common over kitchen sinks and in basements.

Slider. Sashes that glide horizontally. Simple hardware, and useful where an outswinging sash would collide with a walkway or deck.

Tilt-and-turn. A European design whose hardware lets one sash either tilt inward at the top for ventilation or swing fully inward like a door. Excellent sealing and easy cleaning, less common in American homes, and usually a premium line.

Balance. The spring or spiral mechanism inside the jamb that holds a hung sash wherever you put it. When a window won’t stay up, this is the part that failed.

Install and code language

Insert replacement. Also called a pocket or retrofit install: the new window fits inside your existing frame, which stays in place along with the interior and exterior trim. Less money, less disruption, slightly less glass area at every opening.

Full-frame replacement. Everything comes out down to the rough opening, so the crew can see and repair the framing before setting the new window. More money, and the only right answer where there’s rot or water damage.

Rough opening. The framed hole in the wall itself, with no window in it.

Flashing. The layered materials that direct water away from the opening and back out. Invisible when done right, expensive when skipped.

Egress. The code requirement that certain rooms, bedrooms especially, have an opening a person can escape through and a firefighter can enter. Minimum dimensions come from the code edition your municipality has adopted, so confirm locally rather than trusting a number from any article.

HIC number. The Pennsylvania Home Improvement Contractor registration number, which should appear on your contractor’s paperwork.

How to use this while reading a quote

Read a quote with three questions in hand. Does it name the exact product line and glass package, with a U-factor for that combination? Does it say insert or full-frame, opening by opening? And does it list what’s included — trim inside and out, insulation and sealing, disposal, cleanup, and permits if required?

Then use the vocabulary out loud. Ask what spacer the units use and whether it’s a warm-edge type. Ask whether the grilles sit between the panes or on the surface. Ask what happens if the crew finds a soft sill. The answers tell you how well the person across the table knows the product, which is worth as much as the numbers themselves.

A good contractor enjoys these questions. That’s part of what vetting is for: our free matching form connects you with one local pro who will sit with your quote line by line, at no cost and with no obligation to buy.