High performance windows can make a significant difference in the efficiency and comfort of a home. They come in all shapes and sizes. Care must be taken to make sure the windows installed are the best suited for your region.
The National Fenestration Rating Council (NFRC)has developed a window rating system based on whole window product performance. It is important to look at the whole window, not just if it is double paned or someone said they are “insulated”. It is also necessary to consider things like the climate zone you live in and which direction the window is facing.

The NFRC label provides the only reliable way to determine energy efficient properties these windows and other products. The NFRC label appears on all fenestration products which are part of the ENERGY STAR program.

What Does the Window Label Tell You

• U-Factor

  U-factor measures how well a product prevents heat from escaping. The rate of heat loss is indicated in terms of the U-factor (U-value) of a window assembly. U-Factor ratings generally fall between 0.20 and 1.20. The lower the U-value, the greater a window’s resistance to heat flow and the better its insulating value.

  Solar Heat Gain Coefficient
  Solar Heat Gain Coefficient (SHGC) measures how well a product blocks heat caused by sunlight. 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 in the house.

• Visible Transmittance

  Visible Transmittance (VT) measures how much light comes through a product. The visible transmittance is an optical property that indicates the amount of visible light transmitted. VT is expressed as a number between 0 and 1. The higher the VT, the more light is transmitted.

• Air Leakage

  Air Leakage (AL) is indicated by an air leakage rating expressed as the equivalent cubic feet of air passing through a square foot of window area (cfm/sq ft). Heat loss and gain occur by infiltration through cracks in the window assembly. The lower the AL, the less air will pass through cracks in the window assembly.

• Condensation Resistance

  Condensation Resistance (CR) measures the ability of a product to resist the formation of condensation on the interior surface of that product. The higher the CR rating, the better that product is at resisting condensation formation. While this rating cannot predict condensation, it can provide a credible method of comparing the potential of various products for condensation formation. CR is expressed as a number between 0 and 100.

For more information on buying and installing the right windows and doors visit ENERGY STAR.