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In the window and door industry this is the single most important item in regards to energy values. As a customer it is a must you understand exactly what a U-Value is and why it is so important. Lets 1st take the exact definition; U-Factor indicates the rate heat flows through a product for each degree of temperature difference between one side and the other. U-Factor is the inverse of R-Value. The lower the U-Factor, the greater a window’s resistance to heat flow, and the better its insulating value.
Now let’s build on this. Ultimately the idea of buying high efficiency windows and doors is to save money. Now how can you tell how good a product is by the U-value? Now just to get an understanding of U-Values we will compare to some basic windows that people understand as well as use car analogies. Let’s start with your classic up and down wooden windows (double hung) most have a single pane of glass in them as well as some type of storm window on the outside. Very Roughly between U.75 to U.65 that is equal to owning a 1950s to 1960s car technology. Now take that same window and put clear insulated glass (two panes of glass sealed together with an air tight space) into that same frame. Very roughly U.58 to U.48, now you have 1970s car technology. Now take that same window and add hard coat low-e with argon between the insulated glass. Very roughly between U.38 to U.33 now you have 1980s car technology. Now take that same window and add a state of the art soft coat low-e with argon. Very roughly U.34 to U.30, now you have a 2000 car technology.
The above statement is not exact by a long shot but at least it gives you some understanding of the ranges you get with U-values. Now just to continue the importance of lower U-value’s, a product that meets energy star must have a U-value of U.35 or lower. So my point is look at the manufacturers U-value. What year car would you like a 1980s or a 2000? I know my 2000 car can run circles around my 1980 Z-28 and my 2000 car is built much better and is much safer. Today’s technology is great. You just need to see who is on-top when it comes to U-values. If you have a window with a U-factor of U.28 or lower, Wow! You have a performer. At U.35 ;I wouldn’t brag about it and yet many well known windows and doors carry these U-values.
Do your research before you buy; it is easy to buy poor performing products. Brand name doesn’t mean anything if it is not backed by a good U-value. Look for the NFRC sticker on the window. It will always list the U-value.
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