Window energy ratings (Energy Efficient Glass)

 

Approximate value of the various changes

Lowering the window U-value

	Approximate improvement
Cavity width from 20 to 16 mm	1.5 kWh/m2/year
Choice of low-E glass	8 kWh/m2/year
Argon gas filing	11 kWh/m2/year
Warm edge spacer	7.5 kWh/m2/year

Increasing the passive solar heat gain

	Approximate improvement
Low Iron glass:	6 kWh/m2/year
Choice of self-cleaning glass	3 kWh/m2/year