The U-value of glass
The U-value indicates the heat loss per second, per m² and per degree of temperature difference between indoors and outdoors. The lower this U-value is, the lower the heat loss and the higher the temperature on the inside of the glass.
For an outside temperature of 0°C and an indoor temperature of 20°C, the inside of single-glazing has a temperature of 5,6°C and of 17,3°C for high yield glass with U=1.1 W/(m².k). Expressed in energy, you save approximately 44 liters of oil fuel or 36³ of natural gas each year when replacing one square meter of single glass with high yield glass (U = 1.1W/(m².k)). Expressed in money, you safe approximately 36 Euros on oil fuel and 23.55 Euros on natural gas (prices June 2012) per m² of glass.
Comparing thermal comfort in Single-glazing, Double-glazing and High-efficiency glazing. The window frame construction is also important. The heat loss via a window frame is also determined by the insulation capacity of the window frames. For metal windows, a thermal break of the window frame is needed. In order to be eligible for the tax reduction, the heat transmission rate of the glass + window needs to have a U-value that is smaller than or equal to 2,0 W/(m².k). Demand of your installer the guarantee that the placed combination of glass + window meets the requirements of the tax measure.