Rating Systems
To save money on energy costs is the number one reason why homeowners replace their windows. Fortunately there are energy efficient rating systems available to homeowners used to compare windows, exterior doors and other exterior building components.
U-Value
While shopping for windows, most likely you will find an energy efficient label with the term U-value on it. In a typical insulated window you have the two panes of glass, the space between the glass, the frame material and usually weather-stripping or sealant that hold it all together. U-values rate how much heat is conducted through this entire unit – or how much heat is allowed to pass through it.
R-Value
A more familiar term for rating a window’s energy efficiency is R-value. R-values are used to rate how well a material such as insulation resists the flow of heat through it. A window with a high R-value means it will resist heat loss more and therefore be more energy efficient.
What Ratings Should You Look For in an Energy Efficient Window?
A high R-value indicates good energy efficiency - R-19 is better than R-11, for example - and a low U-value indicates good energy efficiency - U-0.35 would be better than U-0.43.
Recommended Levels of Insulation
To get the best possible amount of insulation you need to estimate what the cost of heating or cooling your home will be over the life of the house and then compare that with the cost of insulation. For more advice on how to do this, we recommend browsing The U.S. Dept. of Energy website.