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What Does u-Value Mean For Windows?

what do u values mean

For many homeowners these days, it can be hard and more than a little confusing to try to understand the different ratings given to windows and doors. Perhaps you have the same problem. Most people will look for the highest energy rating and assume it indicates the window is the best performing option for all categories.

Nevertheless, the energy ratings for windows consists of various measurements, such as thermal transmittance, air leakage and solar factor. It’s important to understand these individual aspects of the overall rating to know whether you are getting the best and most energy efficient windows possible. In the following post, we will help you understand one particular rating that leaves customers scratching their heads a little – the u-Value or thermal transmittance.

Why Does it Matter?

The reason there is so much emphasis placed on the various energy-efficiency ratings related to windows is because of the increase in energy prices. As a homeowner, you are undoubtedly looking to save as much money where you can from your energy bills. As well as helping you to save money, looking for energy-efficient windows with a low u-Value will also mean you are helping to do your part to help the planet and environment.

It’s a very common concern – trying to lead greener and more eco-friendly lives. Which is why it’s a good idea to try and understand the various measurements and ratings involved when choosing windows.

u-values saving money

What, Then, Is the u-Value of Windows?

The thermal transmittance, otherwise known simply as the u-Value for windows is the measurement that indicates the rate the heat transfers through a window. The measurement comprises of three different, but equally important, factors.

It is a general rule that windows with lower u-Values are better than those with higher u-Values. Lower u-Values suggest the windows will maintain the interior temperature of a property or home. Recently, there have been changes to the building regulations which mean all new windows must have a u-Value lower than 1.6 w/m2k.

what do u-values mean

How do the u-Value Levels Differ For Windows Compared to Other Surfaces?

Compared to other types of surfaces, there are differences when calculating the u-Values for windows, including the following main factors:

  • PSIG – This is the frame spacers thermal performance
  • Uf Value – This is the window frame thermal performance
  • Ug Value – This is the glass thermal performance

When you combine these measurements, you arrive at the total u-Value for a window.

what do u values mean

Understanding the Measure, A Little Better

You will notice that u-Values are noted with a number that is followed by the letters W/m2k. What does this mean though? Well, the u-Value is calculated as being the watts per square metre per Kelvin.

what do u values mean

Are There Any Situations When u-Values Are Not A Good Idea?

Although, as we have already stated, it is outlined in the updated building regulations that all new properties and homes need to have a u-Value of 1.6 W/m2k or even lower, there are some situations when this lower u-Value might not actually be the best solution. You will find though, that this is only really an issue in areas where there are notably higher temperatures and warmer climates. This is because some of the warm air needs to be allowed to escape the property to prevent the interior of the building from overheating.

what do u values mean

Evolution Flush and Storm Windows

With all the above in mind, the main thing to remember, if you have only taken one thing away from this post, is that you need to look for windows with the lowest u-Value possible. Even if a window has a seemingly high energy rating, from say D to A, and a low u-Value rating, it is not as good an investment as one with both a high energy rating and a lower u-Value rating.

If you are looking therefore, for windows with an extremely low u-Value that meets the building regulations and that are also energy-efficient and have a high window energy rating, you should consider Evolution products. Both the Flush and Storm lines of windows from the Evolution Windows range have the extremely low and preferable u-Values of 1.3 W/m2k.

what do u values mean

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