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What Is U-Value And Why Is It Important?

Energy Savings

“U-value?” we hear you ask. “What’s that?” Don’t worry! The Window Geeks are here to tell you.

Let’s begin with understanding the concept behind a window U-value. It's all about energy efficiency and heat, and how easy it is to escape from your window. Like the R-value is the thermal resistance of a wall, the U-value is the thermal resistance of a component such as a window. Technically they are the same thing, however, the U-value is the inverse of the R-value. To put it in simple terms it is 1 divided by the R-value. But be careful, there are imperial and metric units to watch out for. R-Value is Imperial, while RSI is Metric, and both have a U-value equivalent.

"Can you give some examples?"

Sure! Here's an example of how to convert an R-value of an exterior wall to a U-value:

R21 Wall Insulation (1/21) is 0.048 U-Value in Imperial terms (USA). If I multiply this value by a factor of 5.678 you get a metric U-value of 0.27.

...Now let’s look at it from a window perspective.

1.4 Metric U-value, when divided by 5.678, is an imperial U-value of 0.25, which is an R4 window.

The challenge with U-value numbers is we tend not to apply the units of measure with the number and mix up metric and imperial U-values. The units for metric are W/(m2K) and the units for imperial are BTU/(hrFf2).  Note the use of meters in the metric unit and feet in the imperial unit.

A common comment I get is “your window has a U-value of 1.47 while these other windows have a U-value of 0.30. This is a classic metric/imperial mistake. A U 0.30 is actually a U 1.7 in metric. 

So here is all the background info.  The funny part is, that now with technology, we can just google it - but now you know. Stay tuned to the #WindowGeeks to find out how windows achieve specific U-values.

We Are Your Certified Window Geeks!

We love to talk windows! We’re here to help, so if you have a question about your window project all you have to do is reach out. Contact us early in the process so that our experts can make sure everything is correct from the get-go.

For more information on this topic (and many more!) contact our local Employee Owners at 1-888-534-3333 or drop us an email at Join the club and become a Window Geek yourself by signing up for our biweekly newsletter, which provides news, advice, and tips about the window industry and upcoming events, and test your window knowledge by following us on LinkedIn and Twitter.

Written by: Les Ferris , July 14, 2021
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