As a rule, you can assume that around 35% of a house's heat escapes through the windows. The extent of the heat loss depends on the glazing, among other things. It all depends on whether the window has single, double or triple glazing, the type of glass used and the gas filling between the individual layers. At the same time, penetrating sunlight often contributes to high costs, as a building then has to be cooled in the summer months, which is energy-intensive. The balance between warm and cold, summer and winter, is made easier by the right glazing.

What is the g-value?

The g-value indicates how much solar heat (infrared radiation) penetrates a buildingA low g-value indicates that only a small amount of solar energy penetrates into a building. The g-value can be improved, for example, by providing the outside of the window with an IR-reflective coating that reflects the heat radiation. The idea behind this is, on the one hand, to reduce the costs of cooling the building and, on the other hand, to improve the indoor climate for buildings without comfort cooling. Untreated insulating glass has a g-value of around 1.3.

What is the U-value?

The U-value indicates how much heat escapes from a building, e.g. over windows, walls or roofs. The U-value is often measured for the entire window construction, including the frame and casing. The lower the U-value, the better the window insulates. The U-value can be improved if the glass is provided with a metal-based coating that reflects the long-wave radiation back into the room. A U-value of 1.0 means a heat flow of 1 watt/m2 surface for each degree of difference between the outside and inside temperature (W/m²°C, previously known as the K-value). Modern insulating glass can have a U-value of 2.7 to 0.4.

What does the U-value mean in practice?

In a normal single-family home there is about 30 m² of window glass. The owner chooses between insulating glass with a U-value of 1.2 and glass with a U-value of 1.6. What is the difference in heating costs per year?
Theoretically, a difference in the U-value of 0.1 units amounts to around 9 kWh/m² of glass per year. The difference between 1.6 and 1.2 is 0.4 units. The saving is then (U-value difference) x (additional consumption) x (glass area) = 4 x 9 kWh/m² x 30 m² = 1,080 kWh/year.
At an energy cost of €0.13/kWh, the difference is €140/year. A school with a window area of ​​300 m² would save around €1,400/year in heating costs if they chose panes with a U-value of 1.2 instead of 1.6.

What is the U-value of Hammerglass?

Hammerglass Insulate 3-ply achieves a U-value of 0.66. Hammerglass Insulate 2-ply achieves a U-value of 1.53.