What the NFRC is
The National Fenestration Rating Council (NFRC) runs the certification program that rates the energy performance of windows, doors and skylights in the United States. A certified product line carries a temporary label on the glass showing its ratings, and each certified configuration is listed in NFRC's Certified Products Directory (CPD), which is where the label's CPD number points.
The ratings on the label
| Rating | What it measures | Better is | On the label |
|---|---|---|---|
| U-Factor | How well the whole product keeps heat in (Btu/h·ft²·°F) | Lower | Mandatory |
| Solar Heat Gain Coefficient (SHGC) | Share of the sun's heat that comes through, 0 to 1 | Depends on climate | Mandatory |
| Visible Transmittance (VT) | Share of visible light that comes through, 0 to 1 | Higher, for daylight | Mandatory |
| Air Leakage (AL) | Air that passes through the product, cfm per sq ft; often shown as ≤ 0.3 | Lower | Optional |
| Condensation Resistance (CR) | Resistance to interior condensation, 1 to 100 | Higher | Optional |
The label also names the manufacturer, describes the product (series, operating type, material) and the glazing (glass types, gas fill, grids), and carries the CPD number for that exact configuration. ENERGY STAR is a separate program that uses the NFRC-certified U-factor and SHGC to decide qualification by climate zone.
Why one window line needs many labels
Ratings are for the whole product as configured, so anything that changes the heat or light passing through it changes the label. The usual movers in a vinyl window plant:
- Glass package. Clear glass, a standard Low-E coating and a premium Low-E coating each rate differently.
- Gas fill. Air versus argon changes the U-factor.
- Grids between the glass. Grids block some light and solar heat, so they lower VT and SHGC.
- Operating type and frame. A single hung, a slider and a picture window in the same series are rated separately.
A real example: one vinyl single hung with a Low-E/clear, argon-filled sealed unit is certified at U 0.29, SHGC 0.29, VT 0.55. Add grids and the same window is a different CPD entry at SHGC 0.26, VT 0.49 — the U-factor unchanged. Print the gridless label on the window with grids and the label overstates both numbers.
Printing the right label per window
Because the label depends on the exact selection, the reliable way to print it is from the order itself, per window, after the glass and grid choices are final — typically at QC, just before the window is wrapped. The things that go wrong are predictable:
- Printing from a default. A label drawn from the series' standard configuration is wrong for every window that was not standard.
- Missing a selection. If the lookup ignores grids (or color, where it affects the rating), every window with that option gets its sibling's label.
- Inventing a number. A configuration with no certified rating must not get a label at all. A plausible-looking number stuck to the glass is a certification claim nobody made.
- Two answers. If two certified entries could both match a window, a person must decide — the system must not pick one silently.
How Extrusia handles it
Each certified configuration is stored with the selection it covers — glass, gas, grids and any option that changes the rating — and its CPD number, U-factor, SHGC, VT, air leakage and condensation resistance. At QC the NFRC certificate prints per window on a Zebra label printer, read from the window's own order. No matching rating means no label: the print is refused naming the glass, and a batch prints what it can and reports the windows it could not label, so nothing is guessed. Two equally specific matches are refused too, for a person to resolve.