U-factor
How readily heat moves through the rated complete product; lower indicates less heat transfer.
Lower number = less heat flow through the rated window assembly.
HOMEFRONT COMPASS / MATERIALS & PERFORMANCE RESEARCH
A window has
more than a view.
U-factor, solar heat gain and daylight describe different aspects of a window. Learn what the numbers on an NFRC label mean, then record two products' ratings side by side—without pretending one value alone makes the decision.
Open the label worksheetTHE IMPORTANT DISTINCTION
One label.
Different questions.
NFRC rates defined window configurations using standardized methods. A label is valuable because products can be compared on the same type of measurement. But a lower U-factor isn't a noise rating, a lower SHGC doesn't tell you how much daylight enters, and none of these three numbers alone determines how a particular room will feel.
Confirm each manufacturer's exact product and configuration through the official NFRC directory. Climate, orientation, glazing, frame choices and installed building conditions still matter.
THE THREE PRIMARY LABEL NUMBERS
Understand each measure.
Solar Heat Gain Coefficient (SHGC)
How much solar heat the rated product permits to enter; lower is less solar heat.
Lower number = less solar heat gain in the NFRC test conditions.Visible Transmittance (VT)
How much visible daylight passes through the rated product; higher transmits more light.
Higher number = greater daylight transmission in the rating.These are explanations of what ratings measure, not product-selection criteria for an unknown property. Sound-control metrics, safety glazing, operation and weather-integration are different questions not answered by these numbers.
COMPASS / RESEARCH SHEET 05
Compare labels.
Not marketing promises.
Copy values only from actual product labels. These are your unverified notes—not an official product search, laboratory rating, energy-savings estimate, or determination of which window suits your home.
THE PRIMARY-SOURCE SHELF
The rating isn't the whole project.
Open official references to confirm the manufacturer's exact label and learn what it measures. HOMEFRONT doesn't certify windows, guarantee comfort, or interpret code requirements from this tool.
National Fenestration Rating Council — Reading the LabelFirst-party interpretation of U-factor, SHGC, VT and related product ratings.NFRC — Official Certified Products DirectoryCheck specific manufacturer, product and configuration records with the certifying organization.U.S. Department of Energy — Window Types & TechnologiesFrames, glazing, spacers and installation context beyond three label values.
CONTINUE THE RESEARCH
Look past the glass.
When you're ready to compare actual written installation proposals, read the details surrounding the opening and surrounding wall—product labels cannot settle flashing, exclusions or concealed conditions.
Updated · Sources: NFRC and U.S. DOE, reviewed for educational use. No property-specific recommendation is made.