Understanding The Information on a Window/Door Sticker

Here is a brief explanation of what all those numbers and codes mean on the NFRC sticker that is on new windows & doors.

NFRC Label


The rate of heat loss is indicated in terms of the U-Factor. The lower the U-Factor, the better the window insulates. Energy Star approved windows and doors must have a U-Factor that is 0.32 or lower.

U Factor Picture

 Five Important Variables in Every Insulated Glass Unit

*Type of glass
*Type of Low-E coating
*Type of sealant system
*Type of spacer system
*Its maintenance-free characteristics

Air Leakage

Heat loss and gain can occur by air leaking through cracks in a window. The air leakage rating {AL} is the equivalent cubic feet of air passing through a square foot of window area. The lower the AL, the less air will pass through cracks in the window. Select windows with an AL of 0.30 or less.

Solar Heat Gain CoEfficient

Solar Heat Gain Picture

The SHGC is the fraction of incident solar radiation admitted through a window, both directly transmitted and absorbed and subsequently released inward. SHGC is expressed as a number between 0 and 1. The lower a window’s solar heat gain coefficient, the less solar heat it transmits.

Condensation Resistance

Condensation resistance {CR} measures how well a window resists the formation of condensation on the inside surface. CR is expressed as a number between 1 and 100. The higher the number, the better a product is able to resist condensation.

Visible Transmittance

Visible transmittance {CT} indicates the amount of visible light transmitted through the window. VT varies between 0 and 1. The higher the VT, the more light is transmitted. A high VT is desirable to maximize daylight.