WER Energy Rating | ZEN Windows

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) scale

Here in the UK, the Window Energy Rating (WER) scale is used to measure the energy efficiency of windows, including double and triple glazing. The WER system provides a rating scale from A++ (most efficient) to G (least efficient), similar to the energy efficiency ratings used for appliances.

The rating takes into account things like:

How well the window keeps in heat
How much air leaks through it
How much sunlight it lets in

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.

Windows Energy Rating (WER) Energy Scale

What Affects a Window’s Energy Rating?

There are several key elements that affect the WER. Here’s what makes the biggest difference:

Fixed windows (which don’t open) often have better energy ratings because they’re sealed tighter, reducing air leakage.
Double- or triple-glazing with features like low-E coatings and gas fills boosts insulation.
Warm edge spacers reduce heat loss and condensation around the edges of the glass.
uPVC is a natural insulator, making it a great choice. Aluminium frames need thermal break technology to stop heat escaping.
Thermal breaks are insulating barriers—usually plastic or polyurethane—placed between the inner and outer parts of an aluminium frame to reduce heat transfer.

FAQs

How can I use WER to choose the right windows?

Look for windows with a higher WER rating as they are more energy-efficient, helping to reduce heating costs and increase your home's comfort.

What is a good WER rating?

A high WER energy rating (like A rated or higher) means the window is very efficient at keeping heat in and reducing energy bills. The higher the rating (like A+ or A++), the more energy-efficient the window is.

Do all new windows have a WER?

Yes, most modern windows in the UK must meet minimum energy standards and will have a WER label provided by the manufacturer.

Are C-rated windows energy efficient?

Yes, C-rated windows are still considered energy efficient, especially when compared to older, single-glazed windows. They offer better insulation and can help in reducing energy bills, albeit not as significantly as higher-rated windows.

How do C-rated windows compare to A-rated windows?

While A and B-rated windows provide superior energy efficiency, resulting in greater heat retention and potentially more significant savings on energy bills, C-rated windows still offer a good balance between performance and cost. They can be a more affordable option while still providing noticeable improvements in thermal comfort.

An example of a C-rated window might be one which is double glazed, with a uPVC frame but with an aluminium spacer bar between the panes, and low-E glass being the only sealed unit upgrade.

Upgrading this C-rated window to an A-rated window would typically require upgrading the spacer bars to warm edge spacers and upgrading to argon gas (which would be hermetically sealed between the panes).

Upgrading this window to A+ rated would typically require an additional upgrade to low iron glass for the outer pane.

Is triple-glazing worth the extra cost?

It really depends on what you’re looking for. Triple-glazing offers slightly better insulation and better noise reduction compared to double-glazing, so if your priority is maximum energy efficiency or creating a super-quiet home, it can be worth the investment.

That said, double-glazing is already an excellent option for most homes, especially here in Bristol, where the winters aren’t too extreme.

If you’re planning to stay in your home for a long time, the extra cost can pay off over time with lower energy bills. But if you’re looking for a more budget-friendly upgrade, double-glazing is a fantastic choice.

Key Factors

What factors are considered in the WER? The WER takes into account three key factors, these include;

U-value
Solar Gain (G-value)
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! We want to be as transparent as possible and have put this guide together to help inform you.

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.