The whole point of window energy ratings is to inform consumers about the energy efficiency of the windows they currently have in place. It is an initiative which is designed to help the British public save money on their energy bills while also reducing the nation’s CO2 output. The British Fenestration Ratings Council (BFRC) dreamed up these ratings in 2004 and they are based along the same lines as household appliance ratings. The system goes from A-G with an ‘A’ rating being the most energy efficient. With between 25-30% of a home’s heat escaping through windows, the issue of energy efficiency in windows is an extremely important one.
Formula
The energy rating of windows is calculated by a formula which includes the glass’ solar heat transmittance, otherwise known as the ‘g’ value. A combination of the window’s frame and glass are calculated for the ‘U’ rating. The BFRC were forced to introduce a minimum size for windows because contractors were circumnavigating the minimum ‘U’ rating requirement in homes by making the windows smaller. The BFRC has now decreed that every home should have windows with at least a ‘C’ rating.
Gaining Grade A Certification
The quest to achieve Grade A efficiency is a difficult one with most double glazed windows managing a ‘B’ rating. Low-emissivity (low-e) glass is deemed to be the best quality but this alone may not be enough to secure an A rating. This is because the ratings concentrate on the solar gain and heat loss of the glass. Although low-e glass is virtually peerless in terms of maximum solar gain, its heat loss properties are not the best. A window’s rating also depends on the air that’s contained between the glass panes and the material used in the frame. Aluminium for example, is not the best frame to have in terms of energy efficiency.
To gain Grade A efficiency in a window, you have to improve its ‘g’ value without altering its ‘U’ value or improve the ‘U’ value without lowering the ‘g’ value. Using argon in the gap between the two panes of glass will help improve the ‘U’ value while using glass that is low in iron will aid in your quest to improve the ‘g’ value. It is also important to look at other factors such as the ‘U’ value of the frame and the size of this frame in comparison to the glass. It has long been assumed that an A rating can only be achieved by purchasing expensive triple glazing and even more costly krypton gas. However, adding certain features to double glazing can have the same effect.
In summation, Grade A certified windows are the Holy Grail when it comes to energy efficiency. Grade A windows save more energy than any other and could reduce your annual energy bill by around £200. You will recoup the price of the windows within a few years and also be safe in the knowledge that you have massively helped reduce your carbon footprint. All we need are for more UK citizens to follow suit and this nation will be among the world leaders in household energy efficiency.
