All About Air Leakage Ratings for Windows

Air leakage or air infiltration ratings are a crucial factor to consider when comparing energy efficiency in replacement windows. Usually, people misinterpret these ratings. This article will guide you in understanding good ratings and what to watch out for when comparing your options.

air leakage window

To understand air infiltration ratings, you need to understand what the numbers represent. The industry calculates air leakage in cubic feet per minute per square foot. That is, the amount of air in cubic feet that can pass through a window per minute at a constant rate of 25 miles per hour, divided by the total area of the window.

How Leakage and Air Infiltration Ratings are Often Misinterpreted

Manufacturers always look for a way to tell homeowners that their products are better than others, and taking advantage of air infiltration ratings is a common way to do that. One company might compare their window to another one from a different company with a different size and a higher air infiltration rating.

But since the window is of a different size, it will have a different infiltration rating. When shopping for replacement windows, always look out for such factors so you understand what you’re buying.

Another factor to consider is that the air infiltration rating is based on a constant speed of wind of 25 miles per hour. Despite where you live, you can assume that your windows won’t be constantly bombarded with that kind of wind speed.

Why is Air Leakage a Vital Rating?

For obvious reasons, the amount of air passing through a window is a critical rating. However, you shouldn’t bank on everything you hear. Besides, the NFRC doesn’t even recognize air leakage ratings below 0.1.

The reason is when these numbers are that low, there is no significant difference between one window and another. And the NFRC considers this difference insignificant so you won’t be able to differentiate them.

Again, air infiltration isn’t a required window rating, and some companies completely neglect it. You should watch out for these signs if a company won’t display their windows air leakage rating. You should understand as much as you can about windows before installing them in your home.

window installation done by a professional

As long as the air leakage rating is below 0.3, the NFRC, AAMA, and Energy Star consider it an energy-efficient window. Good energy efficient windows often range at 0.1. High-quality vinyl windows usually achieve much lower rates than 0.3.

For vinyl double-hung windows, anything below 0.05 is an excellent rating. Picture windows and casement windows rate even lower than this, and sliding windows are usually the worst of them all.

Composite, wood, and fiberglass windows typically cannot attain as tight of a seal. Thus, these products usually have much higher air leakage ratings. So, when considering these options, keep in mind that fiberglass, wood, and composite windows typically have significantly worse air leakage ratings.

Air infiltration is a tricky window rating that can be misinterpreted. But you shouldn’t overlook it since every factor of a window is essential, particularly when trying to save money, which may be one reason most homeowners replace their windows.

Factors to Consider When Looking at Infiltration Ratings

It is prudent to avoid putting too much trust into statements from individuals who are drastically oversimplifying things. For instance, if a sales person tells you that his windows achieve a rating of 0.01 and that every other product from other companies will make your house drafty, then they’re probably telling you a lie.

As stated above, for vinyl windows, any rating below 0.05 is excellent, and most likely, you’ll never know the difference. As a fact, the NFRC doesn’t give scores below 0.10 since they believe that below this point, the air leakage measurements can never be accurate. And if this independent testing body in the windows industry doesn’t publish ratings below 0.10, then this is a good sign that you should not worry about it below that point.

Crucial Factors to Remember

Here are a few things you must remember about air leakage ratings:

When window shopping for replacement windows, ensure you pay attention to all window energy ratings. If you come across a company that’s trying very hard to sell you windows based on a single rating such as air infiltration or U-factor, then most probably they fall short in other categories. So, do thorough research, and when in doubt, consult a window expert for advice on choosing and installing your windows.

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