U-factor: The Easiest Way to Distinguish a Good Window
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U-factor: The Easiest Way to Distinguish a Good Window

We get asked all the time, “Is there an easy way to weed out the cheaper windows?” I get it, they all look similar. And, if not educated, it is easy to mistake quality for flashy sales gimmicks.


There is one question (that anyone can ask), that can separate the cheap stuff from the good stuff. “What is the U-Factor of the window?” It’s that simple! Most salesmen focus on the SHGC rating which measures how much direct sunlight heat the Low-E glass reflects. That’s great, but let’s be honest, not every window even gets direct sunlight. Yes the SHGC is important in Texas, but not as important as the insulation value of the window. Whether it’s 100 degrees or 32 degrees outside, you want to keep the inside of your home as constant as possible. In fact, this value is of increased importance in the winter because of the larger difference in temperature. For example, if you keep your home at 75 degrees, a 100 degree day is only 25 degrees different. But, in the winter, a 32 degree temperature outside is 43 degrees difference!


“So, what is the optimum U-Factor rating? Well, according to the energy star ratings system, if a window has a U-Factor of .27 or less, it is rated as efficient in all 50 states. So, by using those guidelines, any window of .28 or greater really isn’t effective enough in cold conditions. It’s good enough in the summer for that 25 degree difference to be rated energy star south, but in the winter time you're likely to notice the shortcomings. My experience concurs with this. Cheaper windows have decent Low-E (SHGC) ratings. (Low-E is a low cost option to add into the glass), so it's basically a standard minimal charge additive. But, for a window to add insulation value, it needs a few things. Thicker glass, larger space between the glass, and Argon gas. Argon gas alone can put most windows under the .30 mark with a slight mark up, but a thinner window means thinner insulated glass units and thinner glass.


In summary, if a vinyl window has a U-factor of .27 or less it is rated energy star all 50 states, and is a really good way to easily cipher out those cheaper quality windows. Some windows go a step further with the insulated frames which can drop the U-factor to .25. A really good triple pane window will go even lower with .22 for a double hung (or .20 for a picture) which is technically rated R-5 by the Department of Energy. All this is quite impressive when compared to the old aluminum windows with an R-Value of 1 or less.



Note from the author:

It is worth noting that we do realize the difference from .27 to .28 is very, very small. But, the point of the article is the easiest way to determine if a window has better quality components than another. That small difference between the .27 and the .28 (arguably) seems to be that fine line for window manufacturers. It is based on simple observations from dozens of branded windows we have used and researched. It is not a one size fits all, and we understand that there are a lot of other factors and options that actually determine the overall quality of a window, and just as important, is the way the window is installed. So, before fussing and rebutting, please remember the purpose of the article. :)


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