In general, it can be assumed that approximately 35% of a house's heat escapes through the window areas. The extent of heat loss depends, among other factors, on the type of glazing. It matters whether the window is single, double, or triple glazed, what type of glass is used, and what gas filling is present between the individual layers. At the same time, incoming sunlight often contributes to high costs, as a building must then be cooled energy-intensive during the summer months. The balance between warm and cold, summer and winter, is facilitated by the right glazing.

What is the g-value?

The g-value indicates how much solar heat (infrared radiation) penetrates into a building. A low g-value indicates that only a small proportion of solar energy enters a building. The g-value can, for example,can be improved by applying an IR-reflective coating to the outer side of the window, which reflects thermal radiation. The purpose is, on 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. An untreated insulating glass has a g-value of approximately 1.3.

What is the U-value?

The U-value indicates how much heat escapes from a building, e.g., through windows, walls, or roofs. The U-value is often measured for the entire window construction, including the frame and reveal. The lower the U-value, the better the window is insulated. The U-value can be improved if the glass is coated with a metal-based coating that reflects 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 outside and inside temperature (W/m²°C, previously referred to as K-value). A modern insulating glass can have a U-value ranging from 2.7 to 0.4.

What does the U-value mean in practice?

In a typical single-family home, there are 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 U-value of 0.1 units accounts for approximately 9 kWh/m² of glass per year. The difference between 1.6 and 1.2 is 0.4 units. The savings are 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 amounts to €140/year. A school with a window area of 300 m² would thus save approximately 1.Save €400/year on heating costs by choosing panes with a U-value of 1.2 instead of 1.6.

What U-value does Hammerglass have?

Hammerglass Insulate triple achieves a U-value of 0.66. Hammerglass Insulate double achieves a U-value of 1.53.