How to Read Your Window Labels and Understand the Label Ratings

Image credit to Consumer Reports Magazine, May 2019

With so much talk around keeping your home energy efficient, it’s important to make sure the windows you install in your home perform the way you want them to. From understanding the product information label to deciphering what condensation resistance means, we’ve got a brief run down on the five major things you need to know when it comes to your window label. 

Product Information Section

This is usually the top part of your label or a large block in the center of your label. It will breakdown every element of your window.

It will include the following:

The manufacturer’s name.

  • This is in case you need to contact them with any questions or issues. 

The window frame material.

  •  This could be vinyl, fiberglass, aluminum, wood, or wood-clad.

Glazing type.

  •  This is either single, double, or triple pane glass.

Window operating style.

  • This is either sliding, double-hung, casement, or awning.

Low-E coating, if applicable to your window type.

  • This stands for low emissivity (or low-e glass). Low-E glass has a microscopically thin, transparent coating that reflects long-wave infrared energy or heat. Some low-e’s also reflect significant amounts of short-wave solar infrared energy. If possible, purchase glass with this coating. 


Visible Transmittance Label

This number will be somewhere to the left of your label and clearly labeled. It will tell you how much visible light passes through the window. The closer the number is to 0, means the less light that passes through the window.


Air Leakage

This number will be properly labeled somewhere below your window’s product information or to the right of your visible transmittance label. This tells you how much heat gain and loss occurs through cracks in the window assembly. The closer the number is to 0, the better.


Condensation Resistance

If you’re concerned with mold growth, this is what you want to keep an eye out for. The numbers can range from 0 to 100 and the higher the number, the better the window is at resisting condensation, which ultimately means less possibility for mold and mildew growth.


U Factor

This is where you will learn how well your window prevents heat from passing through your home.  The numbers can range from 0.02 to 1.20. The lower the number means the better value you are receiving. 

It’s important to not only purchase reliable products, but understand what you are installing in your home. Proper and quality installation is key and if you’re unsure about how to go about installing windows or have a question about your label, give us a call today at 919-379-5767. We’re happy to help!