• Energy Star windows can save you money.window image by Rui Vale de Sousa from Fotolia.com
  
  Energy Star is a program backed by the federal government to help consumers figure out which products will save them the most in energy dollars and to help the public in general by reducing greenhouse gases and other pollutants. The U.S. Environmental Protection Agency sets the standards a product must meet to earn the Energy Star label. Windows earn the label by meeting several requirements.
  
  

Geography

• Geography counts when it comes to windows. A window that earns an Energy Star label in Florida may not qualify for the label in Maine. For Energy Star purposes, the country is divided into four geographic regions: Northern, North-Central, South-Central and Southern. Each area has its own requirements. The regions are decided more by climate than actual geographic location, so parts of Arizona and New Mexico actually fall into the Northern region. A map of the regions is available on the Energy Star web site.
  
  

U-Factor

• The National Fenestration Rating Council (NFRC) must certify windows with a particular U-Factor for them to qualify for the Energy Star program. The U-Factor tells you how well the window insulates by determining how much heat is transferred through the window. U-Factors generally range from 0.25 to 1.25. The lower the U-Factor, the better a window insulates. In the Northern region of the country, the U-Factor must be at least 0.30. In the North-Central region, it must be 0.32 or higher. In the South-Central region, the key number is 0.35 or higher. In the Southern region, a window can have a U-Factor of 0.60 and still qualify for an Energy Star label.
  
  

Solar Heat Gain Coefficient

• NFRC also measures a window's solar heat gain coefficient (SHGC). This measurement lets you know how well a window will block the heat caused by sunlight. SHGC is measured on a scale of 0 to 1. The lower the number, the less solar heat passes through the window. SHGC measurements usually range between 0.25 and 0.80. In the Northern region, anything goes. In the Southern part of the country, the SHGC must be 0.27 or above. In between, the SHGC must be at least 0.40 in the North-Central part of the country and 0.30 or above in the South-Central region.
  
  

Additional Performance Ratings

• NFRC stickers provide other information that consumers may find useful. The visible transmittance rating lets you know how much light passes through the window. Higher numbers mean more light. The air leakage rating lets you know how much air passes through joints in the window. The lower the number, the less air escapes. The condensation resistance rating lets you know how well the window resists water build-up. Higher numbers mean less build-up.