Energy Efficient Low-E Windows: How do they Work?

If you’re thinking about replacing your windows, you should definitely consider Low-E windows. These windows are treated with a special coating that can do everything from reduce fading of furniture to potentially reduce your energy bills as well. So how do these energy efficient windows work? Read our blog to learn everything you need to know!


How do Low-E windows work?

Low-E Windows


What does Low-E mean?


Low-E stands for Low Emissivity. Emissivity is the ability of a material to radiate energy. Materials that have a strong ability to radiate energy have a low emissivity. In this case, the window is the material radiating (reflecting) the energy in the sun’s rays. So a window with a low emissivity coating is better able to reflect the sun’s rays back out into the environment without letting them pass through into your home.

How does this work?


A good way to think of Low-E windows is like a thermos. The outside of the thermos prevents the exterior environment from affecting the temperature of the liquid in the thermos. The inside of the thermos prevents the temperature of the liquid inside from escaping outside. Low-E windows are the same. They reflect heat energy away from your home, and prevent the heat energy that’s already in your home from escaping.

For a scientific explanation of how Low-E windows work, we have to understand what makes up the sun’s rays. A ray of sunlight contains three different kinds of light, which all occupy different wavelengths along a spectrum. These wavelengths are measured in nanometers, and are:

  • Ultraviolet (UV) light, which is responsible for fading things. (310-380 nanometers)
  • Visible light, which is the spectrum of colors we see. (380-780 nanometers)
  • Infrared (IR) light, which is heat energy. (780+ nanometers)

Ideally, you want a window that lets in as much visible light as possible, while limiting UV light that fades the interior, and IR light that adds heat. This is what a Low-E coating does, and that’s why these windows are energy efficient. The less heat you add to the interior of your home, the less you have to run your air conditioner.

What about in the winter when I want heat in my home?


In the winter, the principle of reflection that Low-E windows work on is shifted to the inside of your home. You’ll have heat energy in your home from your heating system. The Low-E coating will reflect this heat energy back into your home, reducing heat loss. This means more of the heat you generate stays in your home, instead of escaping outside through the window.

To learn more about Low-E windows, contact Schaefer Siding and Exteriors today. We’ve been installing windows in Maryland since 1977. We’re both VSI certified and a CertainTeed 5-Star rated Contractor. Contact us today at 410-781-4028 or email us. You can also visit our website for more information.