Block Glass Window Energy Efficiency

With windows accounting on average for 25 percent of your heating and cooling costs, the more windows you have the higher that percentage may be. Even though glass block is a building material, for the sake of energy efficiency ratings, it's considered a window. If you want to add to the beauty of your home with block glass windows, energy efficiency is probably a concern of yours.

Energy efficiency ratings take three factors into account. The first is the airflow coming through the window's opening intentionally or the unintentionally leakage via the window. The second is the amount of heat gained through windows by the sun. The last is the amount of non-solar heat loss and gain, or the "U factor" of heat transmission.

A block glass window is one type of window made up of individual glass blocks, or you can also purchase factory-built glass block windows. Some of the manufactured windows may be eligible for the ENERGY STAR program, but if you assemble a wall yourself out of glass block, it's not eligible because it hasn't been tested and certified by the National Fenestration Rating Council.

Even if you're not concerned about ENERGY STAR certification, you should know that the U factor of an average block glass window is 0.51, which isn't low enough by some state's residential energy code requirements. Because the materials of windows affect the U factors, inquire with glass block manufacturers if glazing or other options are available to make your new block glass window more energy efficient or go with manufactured block glass windows and professional installation for maximum block glass windows energy efficiency.