What is the heat factor in windows (Uw Ug Uf Rw)?

The heat factor of windows, also known as the U-value or U-value, is a measure of heat conduction through a window. It determines how well the window insulates the building thermally. The lower the U value, the better the thermal insulation of the window.

The heat factor takes into account the various components of the window, such as the glass, frame and seal. Windows with a low heat coefficient have better insulation and reduce heat losses in the heating season and heat gains in the summer season.

The U value is expressed in units of W/(m² K), which is the amount of heat in watts that passes through a square meter of window area when there is a temperature difference of 1 Kelvin between the inside and outside.

In the context of windows, the heat factor can be referred to by various designations that refer to specific window components or acoustic properties. Here is an explanation of the most common markings:

• Uw (U-value, total U-value): Heat factor of the total or general window. It covers both heat transfer through the glass and through the frame, as well as other structural elements. The lower the Uw value, the better the thermal insulation of the window.
• Ug (Ug-value, U-value glass ): Heat coefficient for glass itself. It reflects the ability glass to transmit heat. The lower the Ug value, the better the thermal insulation of glass itself.
• Uf (Uf-value, U-value of the frame): Heat coefficient for the window frame. It refers to the frame's ability to transfer heat. The lower the Uf value, the better the thermal insulation of the frame.
• Rw (Rw-value, Rw value): Noise reduction index. It refers to the window's ability to reduce outside noise. The higher the Rw value, the better the sound insulation of the window.

The U value is often used to compare the energy efficiency of different windows. When choosing windows, it is worth paying attention to their heat factor and choosing those that provide good thermal insulation and minimize heat loss in the building.