Is Your World Lookin Foggy?

Double pane glass makes for a good, energy efficient window and many people don’t realize that they don’t have to replace their entire window when the glass has failed (fogged) or the glass has been cracked or broken. Glass repair is far easier than complete window replacement and costs far less. Here are some typical questions asked by customers:

What is an IG?

A: IG stands for Insulating Glass Unit. An IG, double pane or thermal pane window is composed of 2 pieces of glass separated by a spacer, which creates a sealed air space between the two panes. IG’s are manufactured as airtight units that resist fogging due to desiccant in the spacer. It’s the air space that creates the insulating properties that makes these units so energy efficient. The size of the air-space determines how efficient the window will be. A window with a ¾” air-space will be more thermally insulating than one with a ¼” air space. Other factors like Low-E or tinted glass can also increase energy efficiency.

Are all double pane/insulating windows filled with gas or Argon?

A: No. Most dual pane windows are simply filled with plain air. This provides a dry sealed air space which reduces heat transfer. Argon gas is less conductive than air and nitrogen and in extremely cold climates can result in a noticeable difference in heat transfer. In warmer climates like Tennessee, however, the additional cost of Argon gas is not as beneficial or even necessary.

Why have my double pane windows failed?

A: All sealed double or thermal pane windows eventually fail. There is no such thing as a window that will last a “lifetime”. Seals can break and leave you in a fog-filled world. Fog found in double pane windows is caused when the seal surrounding the two layers of glass loosens and moisture seeps through and becomes trapped between the layers. Just a pinhole can create foggy windows. A quality wood framed window that is well maintained (caulked and painted regularly) may last 20 -25 years. Aluminum framed windows may last 17 – 20 years; while vinyl framed windows may last 15 years. The degree of the exposure to sun and rain a window gets will determine the IG’s lifetime. Windows facing south or west will not last as long as windows facing north that do not get direct sunshine.

What is safety glass and why do I need it?

A: “Safety glass” or “tempered glass” is a form of safety glass created by heating regular glass then chilling it quickly to create an inner tension in the glass. This tension produces glass that is about four times stronger than regular glass. However when it breaks, it breaks into small pea sized pieces that eliminate the deep wounding cuts caused by glass. Uniform building codes exist for specific applications for residential buildings to ensure safety. Evans Glass Company installs glass according to the required building codes in order to reduce your risk of harm or liability.

What is Low-E and what does it do for my windows?

A: Low-E stands for Low-Emissivity. Low-E coatings are virtually invisible, microscopically thin metallic oxide layers deposited on a specific surface of the glass to reduce heat transfer entering or exiting the window. Low-E can reduce the heat transfer in a window by up to 60% over a non Low-E window.

Is it possible to repair a failed (foggy) window without taking out the entire frame?

A: Absolutely. Many people don’t know the difference between window replacement and glass replacement. Window replacement is replacing the entire window frames and all, down to the rough opening. Glass replacement leaves the frame intact and only involves replacing the glass (IG) part of the window. Most windows frames from wood, aluminum or vinyl are designed so that the glass units can be removed and replaced without removing the frames.

Pros and Cons of Glass Replacement:


  • Cheaper than window replacement
  • Instant results
  • Can be done to virtually any type of window
  • You can upgrade to low-E, tinted, design glass, add or remove internal grids.


  • Doesn’t upgrade your window frames.