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Air Leakage: What Does This Window Rating Mean?

Homeowners who are in the market for replacement windows often only take into consideration features like the U-factor and solar heat gain coefficient (SHGC). These are measurements that indicate the windows’ ability to insulate and regulate heat loss. Other ratings, such as air leakage, are usually forgotten.

As it turns out, this rating is also worth considering. We discuss what air leakage is and why it matters when you shop for new windows.

The Problem of Air Leaks

Many people assume that their new windows won’t allow for drafts. However, anyone should be concerned about this problem as it can negatively affect the home’s insulation. An increase in energy consumption and moisture retention may also be a result of air infiltration.

The Air Leakage Rating

This rating, abbreviated as AL and overseen by the National Fenestration Rating Council (NFRC), pertains to the amount of air that can go through the window assembly itself. It is expressed as the equivalent cubic feet of air passing through a square foot of window area. A lower AL value means that less air will pass through gaps in the window assembly. You can find the rating alongside the SGHC or U-factor ratings on the NFRC label displayed on all our window replacement products. 

Causes of Air Leaks

Air infiltration in new windows may occur as a result of poor manufacturing or poor installation. Windows made of low-quality materials and components won’t meet the minimum energy efficiency requirements. Also, poor installation techniques can lead to leaks on the best windows. Prevent any of these from happening by working with a reputable, manufacturer-certified contractor.

In this regard, turn to Renewal by Andersen® of Des Moines. We offer top-notch windows, patio doors and exterior doors rated to perform well in our local climate. Call (515) 274-9700, or fill out our contact form to request a free in-home consultation. We serve residents of Ankeny and the surrounding areas.


"We are very pleased with the Renewal by Andersen Company we worked with and the finished product. From the sales representatives in the show room, to the installation, to the trim and staining of the trim, to the service, we are extremely satisfied. All of the persons we worked with on this project were very professional. We'd recommend RBA to anyone. Our installer was Craig."

November 20

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