Understanding Window Glazing, U-Factors, and Low-E

Once you have decided on the style and material of your new replacement windows, your next step is deciding on the glazing, U-factor and the low-e coatings you need for your region and fit your wallet. 

Windows can be single, double, or tripled-glazed.  Single-glazed windows have a single pane of glass in each sash and are the most affordable type of replacement window.  However, they may be the most affordable they are not the most energy efficient as they allow an excessive amount of heat transfer, which can increase your heating and air-conditioning costs. 

Double-glazed windows are also known as insulating glass (IG), or thermal glass are more energy efficient and can reduce your home’s energy cost, thus making them more affordable in the long run.  Double-glazed windows are two panes of glass sealed with an air space between them, which acts as an insulation.  The thicker the airspace, the more insulation qualities the windows offer. 

Triple-glazed windows as the name implies have three panes of glass sealed with two air spaces.  These are the most expensive and are not commonly used because they do not offer a significant increase in insulation for the price.  

What does increase double-glazed window’s insulation properties is the type of gas that is used between the panes of glass.  Double-glazed windows that use Argon or Krypton gas do cost more than regular double-glazed windows, but the amount of savings you will see on your energy bills will make up for the expense.  It is important to know that the gases will leach out over time.  However, this occurs very slowly.  In fact, after twenty years, the double-glazed window will retain approximately 90% of the gas. 

Once you decided on the type of glazing you want, your next step, to understand about the U-Factor.  In northern regions and climates, your greatest concern is sealing out the cold.  However, in southern regions the main concern is keeping out the heat.  U-Factor refers to the rate of heat transfer, and solar gain refers to the amount of heat that penetrates the glass.  Below is the recommended U-Factors and Solar Gain for windows in your area.  However, for specific recommendations for your area please consulate with a local reputable window consultant.

Low-E glass has a low-emissivity coating that admits direct solar heart but that blocks long-wave heat reflected from other surfaces such as driveways, parking lots, and buildings as well as other surfaces.  Low-E glass reduces the total heat gain in a room, thus reduces cooling and energy bills.  Low-E glass can also reduce the amount of ultraviolet rays that enters a room. 

There are several types of low-E coatings available, which can allow low, moderate, or high solar heat gain.  In hot climates such as that in the southern regions, a low-gain coating will reduce the amount of direct and reflected heat into a home.  However, in cold climates a homeowner will want a high-gain coating that will allow an increased amount of solar heating to enter the home.