If you’re interested in improving the efficiency of your home, installing energy efficient windows is a great place to start. Energy efficient windows provide greater comfort, lower your energy bills, and can even keep your furniture looking better over time.
If your windows are cracked, then it’s clearly time to replace them. But you may consider replacing your windows even if they’re not damaged, but rather if they are inefficient. Below are some of the factors that you should consider when looking at the efficiency of your current windows:
Solar Heat Gain Coefficient: This describes the fraction of solar radiation that is admitted through the window. If you live in warm climates, then you want this number to be low or your home may get too much heat from the sun.
U Factor: The U Factor is the rate of heat lost through your window. In colder climates, this is a very important factor, because you don’t want to lose the heat you’re generating to keep your home comfortable. But even in warm climates a low U Factor window can save you money.
Visible Transmittance: This is the fraction of visible light that is transmitted through your windows. Generally, you want to look for windows with a high Visible Transmittance and low Solar Heat Gain Coefficient. While this may seem counterintuitive, good windows are designed to allow a lot of light to come through but keep out the solar radiation by limiting the amount of certain types of light rays.
Air Leakage: This factor measures the amount of air that can pass through the tiny cracks in the assembly of your window. You should always look for windows with an AL rating of .30 or less.
Aside from air leakage, optimal ratings for the above factors may differ for you depending on your climate. A great source for identifying the optimal values for your windows is to look for the ENERGY STAR label.