Designed specifically to decrease energy usage
There are five key performance factors that are illustrated on the window energy efficiency label. They can be a little confusing at first glance but they follow the same principle as the labels on electrical goods which most people are now comfortable with. There is, however, one crucial difference. A well-chosen window can actually save you money as opposed to white goods which will invariably have a running cost.
The label is divided into 3 key areas, Rating, Energy Index
and U, G & L values, each displaying important information to consider when
purchasing replacement windows.
1) Rating Value - A, B, C, D through to G
The most frequently discussed and most easily recognised value; commonly referred to as the energy rating. However, this can be a little misleading as the ratings A, B, C through to G are categories and cover a range of values within which there are varying levels of performance. This is why the other areas need to be considered.
We recommend that you purchase the highest level possible; A being the best.
2) Energy rating - (-2kWh/(m2-K))
Potentially one of the key values to consider, the energy rating indicates the amount of energy lost or gained by the window in kilowatt hours per square metre per year. Energy loss is indicated by a minus figure; energy gain by a plus figure.
Example: -2kWh/(m2-K) equates to 2 kilowatts of energy being lost through each square metre of window per year. As the average semi-detached house has 16.9sqM of window (GGF figures), this would equate to the loss of the same amount of energy as leaving a 1kW heater outside for nearly 34 hours running constantly.
We recommend that this figure be as high as possible; zero is good but positive numbers mean you are saving energy and, therefore, money.
3) U-value - 1.5kWh/(m2-K)
This indicates the level of Thermal Transmittance through the glass in kilowatt hours, per square metre per year. It is a contributing factor to the Energy Rating figure above.
Example: 1.5kWh/(m2-K) equates to 1.5 kilowatts of energy being lost through each square metre of window per year. As mentioned above, since the average semi-detached house has 16.9sqM of windows (GGF figures), the result is 25.35kWh of energy lost per year.
We recommend that this figure be as low as possible.
4) G value - 0.47kWh/(m2-K)
This indicates the Solar Factor through the glass in kilowatt hours, per square metre per year.
It is also a contributing factor to the Energy Rating figure above and represents the amount of solar energy gained through the window.
We recommend that this figure be as high as possible. The higher the figure, the more energy is gained from sunlight and, therefore, the more money you save.
5) L-value - 0.00kWh/(m2-K)
This indicates the Air Leakage through the window in kilowatt hours, per square metre per year. Again, this is a contributing factor to the Energy Rating figure above.
With modern technology and construction methods, this value should be zero on all casement windows
We recommend that this figure be as low as possible. Zero is the ideal goal.
With energy efficiency a hot topic in the current market, understanding and considering the energy label is imperative. This will ensure you reduce both your carbon footprint and your energy bills.