Vinyl Replacement Window Terminology

With so many homeowners in the market for more energy efficient windows and doors for their home, I thought I would use this week’s article to cover the more common terms used to describe a window’s ability to insulate your home from the elements. There is an organization called The National Fenestration Rating Council (NFRC). Their purpose is to test each window manufacturer’s product to independently verify the ratings for each test administered. So, let’s discuss each test and what it means.

First, there is the U-Factor. This number represents the rate that heat escapes through the window. Therefore, the lower the U-Factor, the better the window. Most vinyl replacement windows with standard, dual pane glass, have a U-Factor around .5. When you add LowE glass in place of the standard clear glass, the U-Factor comes down below .4. By replacing the air between the panes of glass with Argon or Krypton gas, the U-Factor can be reduced to around .3. The Government’s energy star program requires a window to have a U-Factor below a certain number in order to be energy star rated. You need to find out what that rating is in your particular area of the country. You can start by going to the energy star website. In areas of the country where rebates are given for installing energy star rated products in your home, you will only receive the rebate by proving that your windows have a U-Factor less than the maximum allowed. That proof comes from the manufacturer’s NFRC label affixed to each window.

Another test is called Solar Heat Gain Coefficient (SHGC). The SHGC measures a window’s rate of heat penetration from outside. The lower the number, the better resistance there is to heat getting into the house from outside. There are also air and water infiltration tests. The air test actually tests how much air is able to pass through the window from outside to inside. Therefore, you want a low number. Typically, a .30 is the maximum allowable rate of air infiltration. Water infiltration tests the amount of water and pressure the window is able to resist. Therefore, the higher rating is better for this test. Frankly, i wish they would just rate all tests on a 1 to 10 scale, with 10 being best. Then, you wouldn’t get confused trying to remember which tests should have high numbers and which ones should have low numbers. You can get more information on window testing by going to the NFRC Website .


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