Guardian Industries UK Glass Division

Window Energy Ratings

The Window Energy rating is a guide to identify how energy efficient the windows you choose are.  Created in the same vein as the A, B, C, rating labels commonly seen on fridges, cookers and other home appliances, the window energy rating, defines the performance of a window in a simple A, B, C, label, A being the best and C being the basic level meeting current building regulation compliance.  However how efficient does the label really make your windows?  To understand that you need to understand the factors that make up the calculation. 

So what are the factors?

Air Tightness

This simply measures the air penetration through the window.  Most modern casement windows will score a zero air leakage in this area meaning no drafts from air penetration.

U-Value (Thermal insulation)

This is basically a measurement of the heat lost through your window to the outside.  This is the key performer: the lower this figure the more efficient your windows will be. 

g-Value (Solar heat gain)
This identifies the percentage of solar heat that can pass through a window.  The higher the percentage the more solar heat passes in through the window helping to warm your house at no additional cost. 

For the best Window Energy Rating performance we recommend the use of ClimaGuard A+ Low E glass as this has a carefully formulated performance which achieves the best Window Energy Rating results on the market.

However, when it comes to solar heat gain (g value), this can be difficult to control, for example on your southern elevation you can receive solar heat gains all day, this means that the area can easily over heat, architects normally specify solar control glass that reduces solar heat gain on highly exposed elevations like the south face, the window energy ratings ignore this factor in the equation. 

Therefore, when choosing the right windows for you, consider the potential heat gains from high solar gain windows and the associated window energy rating; look for the window with the lowest U value, as this will always provide the most reliable benefit. 

Just remember that an A rating may not always be best!
For further information regarding the intricate aspects of the BFRC window energy rating calculation please follow the link below

Window Energy Rating Calculation

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