What is good energy? - When it comes to windows and energy there is a lot more to consider than just U-values.  A window is not like a brick wall, where the focus is simply on the ability of that wall to keep the cold out and the warmth in.  Instead, the latest energy-optimised windows can actually contribute more energy to the heating of a building than is lost through the window to the outside.

Windows play a crucial role in reducing a building's heating consumption to the lowest level possible.  Besides the window's basic energy performance, the primary factors to consider in low energy buildings are:

• The windows' orientation in relation to the sun
• Sun screening and shading
• The glass ratio
• Installation methods and thermal bridges
• The number of windows and total window area
• Air tightness

Below is a diagram explaining the window energy terminology:

Further information can be found in the Good Energy brochure.
 

U-values

In simple terms, a window's U-value is the measurement given to the amount of heat allowed to escape through it (heat loss), or in other words, its ability to keep in heat. 

Download our technical note on U-values for further information.