In your home there is one thing most people don't think about changing when trying to "go green". It's your windows. They actually provide views, ventilation, daylighting and solar heat in the winter. Regular windows on the other hand they can cost up to 10%-25% of your heating bill. If you install energy star windows and also hang some curtains it can give your cooling bill a small break. For colder climate you can get windows that are gas filled with low emissivity(low-e). Then for the warmer climate there are spectrally selected coating to reduce heat coming through the window.Typical coating is metal or metallic oxide which act like a barrier to heat. Now if your not in for paying to replace the windows in your home. On U.S Department of Energy website there are some tips that can help. By using this classy glass you can save some energy and money.