Vinyl Replacement Window Terminology

Many people these days are looking for windows and doors that offer them improved energy efficiency.

The variety of terms used to describe a window’s energy efficiency can be confusing. This article will clear up that confusion. Each manufacturer’s window is independently tested by the National Fenestration Rating Council (NFRC). This agency performs several tests to determine the overall energy efficiency of a window. We will discuss the different test and ratings below.

U-Factor
The U-factor number describes rate at which heat is able to escape through a window. The U-factor is approximately .5 for most modern vinyl replacement windows with standards dual paned glass. You can reduce the U-factor to .4 by using LowE glass instead of standard glass. You can further reduce the U-factor to around .3 by replaced plain air between the two panes of glass with either Argon or Krypton gas. To receive the governments Energy Star rating a window needs to have a U-factor below a certain number. There are different rating numbers for various parts of the country. This information is available on the Energy Star web site. Some part of the country offer rebates for installing Energy Start rating products that have a U-factor below what is typically allowed in that area. Each window comes with a manufacturer’s NFRC label that can be used to claim your rebate.

Solar Heat Gain Coefficient (SHGC)
This test measures the amount of heat penetration of a window from the outside. Windows with lower numbers have a greater ability to resist heat penetrating into the house from outside.

Air and Water Tests
There are also tests that examine the infiltration of air and water. The air test examines the amount of air that is able to pass through the window from outside to inside. You want the lowest number possible with this test. The maximum allowable number for this test is usually around .30. The water infiltration test examines the amount of pressure and water the window is able to withstand. With this test the higher the number the better.

It would be nice if all the tests had a simple 1 -10 scale that was easy for everyone to understand. That way we wouldn’t need to remember the individual scales for each test to determine which window was best. If you want more information you can find it on the website for the NFRC.

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