How to Evaluate Energy Efficient Windows

One of the most important things to consider while you’re shopping for windows is how energy efficient they are. The more energy efficient your windows are, the less you’re going to be spending on your utility bills. New windows can also enhance the look of your home -- a nice added bonus.

• Find the window’s U-factor rating. The window is more energy efficient if the U-factor is low. It is best to find a window with a U-factor rating of .35 or less to save the most on your utility bills.


• Search for the window’s solar heat gain reading on its label. This tells you how much solar heat comes through your window and inside your home. The lower the solar heat gain rating the better. Low solar heat gain windows do not allow the sun’s rays to heat up your home, in turn, causing your air conditioner to work harder to cool your home. However, windows with a higher solar heat gain rating will be more energy efficient during the winter. Choose a low or high solar heat gain rated window based on the climate where your home is located.


• Check windows for their air leakage rating. You want the air leakage rating to be lower than .30.


• Find the window’s visible transmittance rating. This will tell you how much light you can visibly see coming through your window. If the rating is higher the window allows more visible light through.


• Figure out what the windows light-to-solar gain rating is. Some windows do not show this rating. However, this reading tells you how much light can come through your window without heating up your home. The higher this number is, the more energy efficient the window is.