The U-value in double glazing and insulation glass

The U-value, also called heat transfer coefficient, indicates how much heat per degree (Kelvin) of temperature difference, per second, per m² is transmitted through a structure. The lower the U-value, the better insulated the structure is. The U-value is used to calculate the insulation value of windows and frames.

U-value glass

The U-value varies by type of glass. Below is a listing of the different types of glass and their typical U-value:

• Single glazing (U-value ± 5.6)
• Standard double glazing (U-value ± 2.9
• HR glass: double glazing with coating (U-value ± 1.9)
• HR+ glass: coated double glazing with a noble gas filling (U-value ± 1.6)
• HR++ glass: double glazing with an improved coating and a noble gas filling (U-value ± 1.2)
• HR+++ glass or triple glass: triple glazing with coating and noble gas filling. (U-value ± 0.9)

The article The difference between HR, HR+, HR++ and HR+++ glass explains exactly what the difference is between the different types of insulating glass.

U-value frame

The U-value of the window frame is different for each type of window frame. Below you can see the u-value of different types of window frames:

• Wooden frame (U-value ± 2.4)
• Plastic window frame (U-value between 1.0 and 2.2)
• Aluminum frame (U-value of ± 6.0)
• Aluminum frame with thermal bridge breaks (U-value from 1.8 to 2.7)
• A super-insulating profile window frame (U-value of ± 0.8)