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A Closer Look At Window Ratings

As a trusted seller of high-quality windows, we understand that window ratings can come across as confusing at first glance. We also know that many companies emphasize ratings to boost their window sales. Here at Window Guardians, we want to be as transparent as the panels that we sell. So, we’ve decided to write a breakdown on some window rating terminology for our customers.

When Lower Ratings are Better


This number measures the rate of heat transfer of your widows, indicating how much heat will be lost or gained through the glass. The U-Value of windows can be estimated from 0.25 to 1.25. The lower this U-Value is, the more energy-efficient your window will be. For windows exposed to a lot of direct sunlight, look for panels with low U-Values.

Air Leakage

This number signifies the amount of air that a window will allow to pass through. The smaller the number, the more airtight the window will be. If you reside in a particularly windy area, you should look for a low air leakage rating. Ratios typically range from 0.1 to 0.3.

When Higher Ratings are Better

DP/Design Pressure

This number is used to show how much pressure a window can take before it breaks. The higher the rating is, the stronger the window. For those that live in areas with frequent storms and heavy winds, look for windows with higher DP ratings. Typical residential rating range from DP 30 through to DP 50.

Condensation Resistance

This rating indicates how much moisture can collect on the surface of a window. It is measured on a scale of 1-100. The lower the number is, the more condensation, which can lead to window damage and increased maintenance. For those of you that live in a humid or wet area, we recommend looking for a higher condensation resistance rating.

Certification Labels

NAMI Structural Certification Label

The National Accreditation and Management Institute (NAMI) is an independent business that inspects and certifies windows. It provides energy performance ratings based on specific values, including U-Factor and other variables. The label should show where the window was tested, and the grade of performance it achieved.

AAMA Certification

The American Architectural Manufacturers Association certifies windows using the tests. These are water leakage, air leakage, and structural strength. Windows tested only for thermal performance receive silver certifications. Windows that are tested for all three variable will receive a gold label.

It’s important to note that not all window manufacturers will test their products using these certifications. However, using the information provided should help you to choose your new windows more wisely.

For more information, click here to visit the Window Guardians website today.