About energy efficient windows: Impact-resistant windows have several different ratings, each of which has varying degrees of money-saving energy efficiency. The ratings can be confusing, so be sure you choose a contractor who will walk you through each one and explain which one would be in your best interest, energy and cost-wise.
What determines the energy-efficiency of glass? There are several factors: the thickness and number of layers of the glass (it can be single, double or triple pane glass), if it has weather stripping, how the frame itself is built, the kind of low-emissivity coating on the panes and the presence of krypton or argon gas.
To help you get started the simplest way possible, we’ve compiled a list of the various energy ratings and what each one means to you.
The U-Value is the one that is most often looked at, although the others are just as important. The U-Value of a window is the amount of heat that would be transferred through the window. This is measured how efficient the glass is at conducting heat. The lower the U-Value, the your windows will be at insulating your home.
The R-Value, or R-Factor as it is also commonly known, is a measure of its resistance to the transfer of heat flow. The higher the R-Value, the more energy efficient windows you have.
Solar Heat Gain Co-Efficient
The Solar Heat Gain Co-Efficient (SHGC) tells you the amount of heat that would go into your house. If you air-condition your home most of the year, this is a measure you’ll want to look at closely. Impact-resistant clear glass typically has a SHGC of 0.72. Bronze is set at 0.55 and gray glass is set at .56. As you would expect, the darker the tint of the glass, less heat will enter your home. You want a lower number here.
This is a newer term to look for in impact-resistant glass products. Low-E is “low emissivity” and is an additional coating that can be applied to glass to increase the energy efficiency of your windows.
This microscopic, metallic coating helps to reflect and deflect heat, keep it inside or out of your home. During winter months, your home will be kept warmer and during summer, your home will maintain its cool temperature more efficiently. All of this combines to reduce your electric bill.