An ‘A rated’ window is one that is exceptionally effective at gaining free heat energy from outside and then keeping valuable heat inside your home.
A window can only be classified as ‘A rated’ if it has been tested by an independent, certified organisation against energy efficiency criteria and been found to meet or surpass the specified requirements.
To enable a window to be classified as ‘A rated’ its various properties are measured and the results are then accumulated into just one simple figure. The figure dictates where the window can be classified on the A to G scale in terms of its energy efficiency. An A rated window is one that achieves an excellent score on this scale.
Many people mistakenly talk about ‘A rated glass’ or ‘B rated glass’. This is largely born from the fact that most people think that the energy efficiency of a window depends solely on the glass being used. This is a common misconception. There is actually no such thing as ‘A rated glass’.
When a window is being assessed to judge its energy efficiency rating a number of factors are considered and measured, not just the glass. The other components of a window that are just as important as the glass are:
- the UPVC being used – including how many internal insulating chambers it possesses
- the reinforcing material being used inside the UPVC to give the window strength
- the effectiveness of the window to form a tight seal when closed – eliminating draughts
- and finally the glass type is considered as part of the overall window composition
The testing procedure to gauge the energy efficiency of a window is designed to not only look at how effective a window is at keeping valuable heat inside your home – it is equally designed to assess how well a window can capture free heat energy from the sun. This free energy is described as solar gain (g). The solar gain factor has a large influence on the overall rating given to a window.