How to understand window energy ratings

posted in: Energy Ratings | 0

Aluminium Windows: window energy ratingsWhen it comes to saving energy, your choice of windows can make a big difference. Windows can be responsible for the loss of up to 25% of the heat in your home – so choosing energy efficient windows is an action that can save homeowners significant costs from their energy bills. Because some windows are more energy efficient than others, Window Energy Ratings (WER) are a way for you to compare the energy performance of different windows to help inform your choice when making a purchase. Here we explain just how the WER work.

What are window energy ratings and how are they measured?

Basic CMYK: window energy ratingsWindow energy ratings grade windows on their energy efficiency from A (excellent) down to G (poor). A standardised rainbow label similar to those used on white goods is displayed to help consumers to easily compare energy ratings for different windows.

The performance of each window is calculated using a formula that measures:

  • Thermal efficiency (the amount of heat that can escape from the window, described as the u-value)
  • Solar gain (how much the heat from the sun affects the heat that comes through the window into the room. Good solar gain will mean you don’t have to use as much energy to heat your home)
  • Air leakage (the amount of air that can escape when windows are closed)

The very best-performing windows will have a low u-value, high solar gain (although in hot countries this would not be such a good feature) and a low air leakage rating (AL). Of course, some of these factors will be affected by the size, position and orientation of your windows, too – things that the window energy rating cannot take into account.

Does the WER apply to the frame or the glass?

You can’t get a window energy rating for either a standalone frame or a frameless window pane. This is because windows will perform differently depending on which combination of frame and glass is used, so window energy ratings can only be applied to a specific pairing of glass plus frame. So, the WER will only apply once you put the frame and the glass together, to give an energy rating to the finished window.

Is there a minimum legal window energy rating?

Yes, there is. Since 2010, Building Regulations have required new or replacement windows to have a WER of C or above. (There is an alternative way to meet the regulations if your windows have a u-value of 1.6 or less, but this is harder to prove). Existing windows may have a lower rating, but if you are looking for replacement windows, you will need to ensure that your new windows have window energy ratings of A, B or C, or otherwise comply with the maximum u-value.

Are doors covered by window energy ratings?

No, there is currently no requirement for doors to be measured or rated for energy efficiency, so doors do not normally display such a rating. However, if well-insulated, thermally efficient doors are important to you, ask your supplier for their recommendations for doors with high thermal performance.

Is a high WER the most eco-friendly option?

Window energy ratings only measure energy efficiency, which is just one aspect to consider if you are concerned about environmental impact. Other factors, such as recyclable materials and eco-friendly manufacturing processes, do not affect the WER. However, all else being equal, choosing an environmentally friendly thermal efficiency for your windows is a great way to save energy and reduce your impact on the environment. Think of it as just one aspect of an environmentally friendly home.

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