Advice on U-values

In general, the frame allows more heat to escape than the glass.  Minimising the frame to glass ratio is the easiest way to improve U-values, so make your windows as large as possible and with fewer mullions and transoms. 

Glazing
VELFAC windows use low-e double-glazed units with argon filled cavities and soft low-e coatings as standard.  The European test window size of 1230mm x 1480mm achieves a U-value of 1.55W/m²k. 

Improvements can be made by using different combinations of additional low-e coatings, Krypton gas, Warmedge spacer profiles and triple glazing.  Some examples can be seen below:

 

Glazing: 4-16-4, argon filled cavity with warmedge spacer and low-e coating on sides 2 & 3.
U-Value: 1.47W/m²k.

 

 

 

Glazing: 4-16-4, krypton filled with 2 low-e coatings on sides 2 & 3, and a warmedge spacer profile.
U-Value: 1.43W/m²k.
N.B. Effect is much better on slimmer cavities

 

 

Glazing: 4-12-4-12-4, argon filled cavities with warmedge spacers and low-e coatings on sides 3 & 5.
U-Value: 1.18W/m²k.

 

 

  

Glazing: 4-12-4-12-4, krypton filled cavities with warmedge spacers and low-e coatings on sides 3 & 5.
U-Value: 1.02W/m²k. 
U-Value: 0.90W/m²k with VELFAC thermal break.