A Guide to Window Energy Ratings (WER)
The Window Energy Rating (WER) is one of the most important factors when buying new windows. Understanding it is quite straightforward when it’s broken down into its core components. Our guide aims to provide you with a clear understanding of what the WER is and how it affects the efficiency of the windows, doors and conservatories in your home.
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Window Energy Rating (WER) system
Here in the UK, the Window Energy Rating (WER) system is used to measure the energy efficiency of windows, including double and triple glazing. The WER system provides a rating from A++ (most efficient) to G (least efficient), similar to the energy efficiency ratings used for appliances.
WERs give you a clear idea of how well a window will keep heat inside your home, potentially reducing your energy bills and increasing your home's comfort.
The WER takes into account three key factors, these include;
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U-value
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Solar Gain (G-value)
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Air Leakage (L-value)
Key Factors
What factors are considered in the WER? The WER takes into account three key factors, these include;
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U-value
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Solar Gain (G-value)
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Air Leakage (L-value)
U Value
The U-value measures how much heat is lost through the window. A lower U-value means better insulation and less heat loss.
This measures the window's ability to transfer heat. Specifically, it shows the amount of heat lost in watts (W) per square metre of window area when the external temperature is lower than the internal temperature. The lower the U-Value, the better the insulation provided by the window, contributing to a higher WER.
Solar Gain
Solar Gain, or G-value, indicates how much solar heat the window captures. A higher G-value can help warm your home naturally, contributing positively to the energy rating.
Solar Heat Gain Coefficient (SHGC) essentially refers to the window's capacity to capture heat from the sun and use it to warm the home. It is expressed as a fraction; a higher G-Value means more solar heat gain, contributing positively to the window's energy rating.
Air Leakage
Air Leakage, or L-value, measures how much air can pass through the window's joints. A lower air leakage means better insulation and energy efficiency. For energy efficiency, you want this value to be as low as possible to minimise unwanted draughts.
What are window energy ratings?
It’s a question that comes up a lot and many companies use energy ratings to try and persuade people that their window is the best and most efficient on the market!
Launched in March 2004, the Window Energy Rating (WER) label is similar to that used on many white goods in our homes, such as fridges and washing machines. The WER rating was introduced to simplify window performance information, whilst simultaneously giving greater detail than customers would have previously had access to, with the only real indicator of performance being the U-value, which is more limited in the value of information it offers, on its own.