Most of the heat in buildings is lost through windows and exterior doors. If a cool airflow is felt near the window or door, most often, the seal needs to be replaced.

From the moment of installation, the seal is exposed to various conditions, therefore, over time, it no longer performs its functions and undesirable airflow occurs. The effectiveness of the window seal can be checked by inserting a piece of paper between the frame and the window. If it can be easily pulled out, heat flows out and cold flows in just as easily. However, even when replacing the seal, it is important to consider the coefficient of thermal insulation "U", which indicates how much heat escapes through a certain area of the structure in a given time and is usually indicated on the manufacturer's label. Attention should be paid not only to the U-value of the window package but also to the total U-value, which includes the window frame.

Seasonal weather changes, improper installation, and poor-quality materials are some of the reasons why heat escapes through windows and doors and you should think about replacing them.

When selecting windows, you should pay attention to several performance characteristics:

• heat insulation,
• air permeability,
• wind load resistance,
• acoustic properties,
• safety class.