Double Glazing U-Values, what are they?
For some time now, energy products have been subject to labeling that identifies how energy efficient they are, and most of us will be familiar with the colorful labels we see on thing like fridges & washing machines.
Windows & Doors are no different in that they need to be energy efficient and you may have seen reference to the U-value of double glazing and wondered what it means.
In short, the lower the U-value, the better the window or doors is at keeping the heat in.
The Window Energy Rating (WER) has a colour coded & alphabetical system to identify the performance. You will usually find blue / green colours at the top and red /brown at the bottom and matched with a letter from A+ down to G – A+ rating is the best, G is the worst.
The rating is designed so that consumers can compare products on a “like for like” basis easily.
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Making Sense of the Label
What the label takes into consideration is based on a standard test and applies to the whole of the window or entrance door, not just simply the glazing. However, as this is a “laboratory test” the product can have different performance in real life – strangely enough, sometimes it’s better.
For your information
- Every new or replacement window should have a rating of C or better.
- The lower the U-value the less heat will escape to the outside
- A higher G-value indicates more “solar gain”. The window lets in more heat than it loses due to the fact that it lets in more light.
- Air infiltration is referring to how much wind leaks in or out of the product
- The product should also contribute to sound insulation and reduction of condensation.
You can often see rating labels from 3 different sources such as:
- CERTASS – http://www.thermalratingregister.org/
- The BFRC – http://www.bfrc.org/
- BSI Kitemark – http://www.bsigroup.com
Something to bear in mind though is that if you super-insulate your home but don’t have adequate ventilation you could actually be building up a condensation problem.
Also if you have a room with a large window that has a lot of direct sunlight for most of the day and the unit has a high G-value, it could mean that the room will get stuffy & overheated in the summer from the effect of solar gain.