Understanding Energy Efficient Windows: Low-E Glass Windows & Energy Star Window Frames


What Exactly Makes it Energy Star? What is Low-E Glass?

The data is here, the numbers are in: heating and cooling your home is, and will become, more expensive. Look at how much your National Grid bill jumped in February!! You know you need to save money on your energy bill, and you know that modern windows can help, but where do you start? Here are some specific questions that people ask about the new generation of energy efficient windows:

  • What is one of the most important details of an Energy Star window?
  • What framing materials do Energy Star windows come in?
  • Moreover, what makes a window low-e?

Never have energy efficient windows played such an important role in making up the difference between saving and spending. Let’s take a closer look at Energy Star windows and low-e glazing so you can decide how you can save next winter.

Energy Star Windows

energystar-windows In the image to the left (from an Energy Star PDF on Qualified Windows), you’ll see that the anatomy of an energy efficient window consists of 5 things in particular. Ultimately these 5 things work together to determine the u-value. The u-value is a way to measure a window’s energy efficiency and to qualify for an Energy Star rating, a window must be tested and verified with Energy Star’s requirements.

Window Frames

Frames are an integral part of attaining a good u-value. Frames come in a variety of makes:

  • Vinyl window frames: these low-maintenance frames are also very poor conductors…which is GOOD, it means they don’t radiate the COLD. While some companies brag that the vinyl frames can be insulation filled, this is somewhat of a gimmick, this adds extremely minimal insulating value, but adds cost. The design and characteristics of the vinyl extrusion is the key. Best value.
  • Aluminum window frames: these are made up of at least 15% recycled content. Oftentimes, these designs have ‘thermal breaks,’ which are made to reduce the amount of conductive heat that can be lost through a purely metal frame. However, aluminum is a better conductor of heat and cold than any of the other materials.
  • Wooden window frames: The classic prototype of window design, and for a reason. These stark frames are natural insulators. The interior will require some maintenance of staining or painting, but the exterior can be made clad with vinyl or aluminum to ensure low-maintenance and weather resistance.
  • Fiberglass window frames: these frames support insulation and are made up of  glass fibers and resin; they the expand and contract on levels coinciding with the glass it frames. Be prepared to pay high prices.

Low-E Glass and Glazing

Before we go into low-e glazing or low-e coating, getting a grasp on the “light spectrum” will put things into perspective. Aside from Visible Light, which we consciously experience, there are many other forms of light. Two of these forms have a direct effect on your home’s interior – ultraviolet and infrared light.

  • Ultraviolet (UV) light, which has a shorter wavelength than visible light and a longer wavelength than X-rays. Overtime, UV light will fade colors on things like dyed fabrics or textiles and painted or dyed walls.
  • Infrared (IR) light, which has a shorter wavelength than microwaves and a longer wavelength than visible light, is what one would see through “heat vision.” Without IR light being effectively hindered, it leaves through windows and comes through windows—this affects the internal temperature of your home during both winter and summer.

The benefit of low-e glazes (or low emissivity glazes) is that the panes have been optimized to minimize the amount of UV and IR light that passes through the glass of modern windows. This has to be done in a way that does not hinder the amount of visible light that shines through. These glazes are efficient, as they reduce the amount of absorption, reflection, and emission that happens when energy takes its natural routes: heat out of your home in the winter, heat into your home during the summer.

Which replacement windows are right for your home?

Clearly, there are many advantages to these energy efficient replacement windows to help you reduce heating costs and improve the value of your home. For more information on windows/doors, consult our projects page or contact us with your questions in mind!