All our windows are rated for their energy efficiency. Many people will be familiar with the ratings that are given to white goods such as fridges and washing machines, which are graded between A - G, depending on their environmental efficiency - A being the best and most efficient. What is less known is that the same system can be applied to windows and doors also!
RATING VALUE (A - G)
This is the most recognisable and visible element of the label, showing clearly the products energy efficiency in coloured bands, from the dark green A (the best rating) through to the dark red G (the lowest rating and therefore the least efficient). Obviously, products valued at 'A' are the most preferable. Building regulations currently stipulate a minimum requirement of 'C' (or a U-Value of 1.6 w/m2K).
THERMAL TRANSMITTANCE (U VALUE)
This indicates the amount of heat energy transmitted through a door or window, set out in watts per metre2 per degree Kelvin. This is a contributing factor to the Rating Value above. The lower the U-Value, the less energy is lost, and the more efficient and economical the unit.
SOLAR FACTOR (G-VALUE)
This represents the amount of solar energy that is gained through the window. The higher the value, the more energy gained and the greater the saving.
EFFECTIVE AIR LEAKAGE (L-VALUE)
This is the amount of air that permeates through the window weather seals, also a contributing factor to the Rating Value above. Modern high performance windows will have a low air leakage rate.