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Air Leakage: How It Affects a Window’s Energy Efficiency

Remember, a one-size-fits-all approach won’t work in choosing a new energy-efficient window. Everyone knows you should look for an ENERGY STAR® certification, but how do you pick one from dozens of windows that have that label? You look at its U-factor, solar heat gain coefficient (SHGC) and air leakage rating (AL) ratings.  

What the AL Rating Means 

The AL indicates the amount of air that can pass through a square foot of a window. A window with an AL of 0.1 lets in the least amount of air while a window rated 0.3 lets in the most amount of air. However, this doesn’t mean you should avoid windows with a rating that’s more than 0.1 – as long as the AL is below 0.3, the window can be considered energy-efficient. 

Here’s a tip: if you’re looking for a window with a low AL, try looking for double-pane replacement windows

How Does It Affect Your Home’s Energy Efficiency?

Of course, drafty windows, ones with a rating of more than 0.3, can raise your power costs; heat and air-conditioned air can leak out of your home, forcing your HVAC unit to consume more power to maintain a comfortable temperature inside. 

How to Pick the Right Window 

However, keep in mind that although a window’s AL is an important aspect, it isn’t the only one. When evaluating window performance, you need to factor in its several other features. One feature can’t make a window entirely energy-efficient. Our energy-efficient windows have a variety of features like Fibrex® frames with excellent insulation capabilities and ultraviolet-blocking High Performance™ Low-E4 glass. 

One more thing: make sure only a qualified company installs your new energy-efficient windows. Installation errors can leave behind gaps, which can then let in drafts. 

Renewal By Andersen® of St. Louis, an independently owned retailer with an A+ rating from the Better Business Bureau, offers a wide variety of premium windows and doors. To schedule a free consultation with one of our design specialists, call us at (314) 983-9977, or fill out our contact form here. We serve homeowners in Chesterfield, MO, as well as other nearby areas.

Reviews

"Have nothing but great things to say about the window installation done today by John Hutchinson with Renewal by Andersen! He was friendly, personable and professional and did a great job installing. He did a great job of putting down roller pads and tarps with next to zero clean up. Would highly recommend them for any window replacement needed!"

Mark V.
Jun 26, 2025

"We had our new Renewal by Andersen windows installed on June 5th & 6th, 2025 and we LOVE them! The quality, beauty, and functionality are best-in-class! The whole experience from dinner presentation at Lazy River Grill, the initial in-home sales consultation and measurement, the regular communications from the salesman and concierge, and the installation team’s professionalism and skills made the process so seamless. This is the second home we have opted for Renewal windows and doors and have been delighted both times! Thank you Renewal by Andersen STL! "

Jeff C.
Jun 7, 2025

"I had an excellent experience with RbA STL. Our designer, Courtney, was great and the finished product is awesome. The installation was easy and the gentlemen left our home cleaner than they found it upon entering. I would recommend RbA STL - you’ll get tired from their constant contacts, and that’s a GOOD thing!"

Jeramy D
Jun 3, 2025

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