Need Energy Efficient Windows? Look For The U-Factor

Posted on: 15 October 2015

Do you need energy efficient replacement windows for your home? There are numerous options available at your local home supply store or window company. The amount of selections can make the shopping process intimidating, but there's one number in particular that can help you find the most efficient window when comparing between similar models. And that number is called the u-factor.

The u-factor measures heat transfer or the rate at which warm air can pass through the window from outside or how much heated air can pass through to the outside. A lower u-factor is better because the rate at which the heat is moving through is also lower.

But what constitutes "low" and which window frame and glass materials offer the best u-factors? 

Highest U-Factor Materials

Wood and vinyl window frames tend to have almost identical u-factors when all other factors, such as window thickness or gas filling, are the same.

The range of u-factors for wood and vinyl windows starts at about 0.38 for double-pane glass and goes down to 0.22 for quadruple-pane glass with a krypton gas filler.  Compare these numbers to the aluminum frame range of 0.81 to 0.53, with the lower end being triple-pane glass as the quadruple isn't available in that material. 

Aluminum frames can be improved slightly with a thermal break, which is insulating material inserted directly inside the frame. The break moves the aluminum u-factor range to 0.62 to 0.36 – still not as good as vinyl or wood but decent enough if an aluminum frame is closer to your price range.

Best Glass Materials for U-Factor

As mentioned above, the type of glass used can help make even the less efficient aluminum more efficient by comparison. There are two primary characteristics to consider with glass: number of panes and type of gas filling.

Double panes are one of the most common types of energy efficient windows as there are enough panes to hold in gas and provide adequate efficiency for most homes. Higher numbers of panes also cost more, but the price cold be worth it if you live in an area with drastically cold or hot temperatures.

Gas filling is an option that adds an insulating gas in between the glass panes. The gas is harmless and clear but thick enough that the heat attempting to transfer through the window is slowed down even more. Argon and krypton are the gases most commonly used and krypton is more energy efficient, and costlier, than argon. For more information, talk to a professional like Fas Windows and Doors.