Q: I’ve noticed that the furnishings in my home are fading from the sun, including my high-quality hardwood floors. My house also heats up a lot during the middle of the day due to intense sunlight. I’m looking into solutions and heard that low-e glass can offer protection from UV rays. How does this work?

A: One of the ways that replacement windows can help save energy is by reducing the UV rays that filter through the glass. Low-e glass is one of the industry-leading technologies for homeowners to block out UV rays, resulting in a more comfortable home.

But what is low-e glass, and do you really need this energy-saving solution?

What is Low-E Glass?

Low-e stands for low-emissivity glass. According to Glass Magazine, it was developed in 1976 as an investment by the Department of Energy. Low-e is a microscopically thin coating that is applied to the window’s glass during the manufacturing process. It has three primary locations on standard double pane insulated glass depending on the product that you choose:

  • The surface that faces the exterior of your home
  • The surfaces that face each other inside of the insulating glass unit
  • The surface that faces the interior of your home

It’s transparent and virtually invisible to the naked eye. This layer or layers are engineered with invisible metal or metallic oxide layers, resulting in an insulating glazing. Although it’s thinner than a human hair, the low-e coating on a window has a big role to play.

How Does Low-E Work?

During the summer, a coating of low-e on your window works to reflect the summer sunlight. It specifically reflects long-wave infrared energy. Some low-e windows on the market also reflect short-wave solar infrared energy.

In the simplest terms, low-e glazing acts like a thermos. A thermos’ silver lining helps maintain the current temperature of the drink that it’s containing. The constant temperature is achieved by the lining’s reflection, which increases the insulation of the thermos.

Even with a small amount of low-e applied on the glass, it essentially works the same way. The coating of low-e reflects the sun back outside during the summer and helps keep it inside during the winter, which ultimately will lower your utility bills.

Measuring the Performance of Low-E Glass:

Just like other elements of energy efficient replacement windows, measurements are included to indicate performance of low-e glass. You can gauge the effectiveness of the low-e coating with measurements including:

  • Solar Heat Gain Coefficient (SHGC): Measures on a scale from 0 to 1 and indicates how well the window blocks heat from the sun. The lower the SHGC rating, the less solar heat it will transmit into your home.
  • U-Factor: Sometimes referred to as U-Value, determines how efficiently the window prevents energy from escaping. It’s generally measured from .2 to 1.25. Low U-Values have the best insulating factors as well as better resistance to heat flow.
  • Visible Light Transmittance: VT is measured from 0 to 1, and it determines how much visible light makes its way through your window. A higher number indicates that more natural light is filtered into a room.

How do I Know if My Windows are Low-E?

Since low-e is an invisible coating, it can be hard to tell if it’s on your windows—but it’s not impossible. You can conduct a couple easy DIY tests to determine if you have low-coating on your window, such as:

  • Holding a lit match or pen light in front of your window. If you have a dual pane window, you’ll find four reflections of the light (two per lite of glass)
  • Once you detect how many glass lites are in your window, the next step is to look for different colors in the glass surface. If there is low-e on the window, one of the images will be a different color than the rest.
  • If there is no low-e coating on your windows, all four glass lites will be the same color.

Low-e glazing does add to the cost of your windows, but this cost will be made up in energy savings. A top rated window with premium glass package has 8 layers of high-performance metallic shields. This type of window can resist photochemical damage (fading of furniture and floors) 140% better than clear glass alone and prevent energy loss by up to 60%.

Protect Your Home from the Sun with Coastal Windows & Exteriors

Coastal Windows & Exteriors has top-of-the-line replacement windows that incorporate today’s top technology for energy savings—including low-e. If you have more questions about low-e or you’d like to discuss installing these windows in your own home, contact Coastal today at questions@mycoastalwindows.com or by calling 978-304-0495.