The window industry measures the energy efficiency of their products in terms of thermal transmission, or U-value. The U-value of windows measures the rate of heat transfer through a product. The lower the U-value of a window, the lower the amount of heat loss, and the better a product is at insulating a building.

Carlson specialises in energy efficient eco windows and doors that have u-values as low as 0.61W/m2K as shown below.

•  The U-values of windows detailed above are for the whole window, including glazing, frame and spacer bars.
• Centre-of-glass u-value (uG) describes the performance of the glazing alone without the effects of the frame.
• For most energy efficient windows, the whole window U-value is higher than the centre-of-glass U-value (uG).