The best way to compare the energy efficiency of windows and patio doors is to look at their NFRC (National Fenestration Rating Council) label. Every product has a label applied to the glass with energy performance ratings that have been certified by an NFRC accredited independent testing laboratory.

1. NFRC certified products – Look for the NFRC logo on the label to be sure the product is certified according to National Fenestration Rating Council requirements.
2. U-Factor – indicates how well a product prevents heat from escaping.  The lower the number, the better.
3. Solar Heat Gain Coefficient – measures how well a product blocks heat caused by sunlight. The lower the number, the more it will help reduce the use of air conditioning and as a result reduce electrical bills and energy use.
4. Visible Transmittance – refers to how much visible light comes through a product.  The higher the number, the more light is transmitted.
5. ENERGY STAR^® – When you see the ENERGY STAR® logo on the NFRC label, you can be certain that the product meets or exceeds ENERGY STAR® performance guidelines in the shaded portions of the map shown on the label.