In winter, heat is dissipated to the outside through ventilation of buildings. This heat can be recovered from the ventilation air with controlled ventilation, in which the air is forcibly extracted and the clean air is blown in. By means of a heat recovery installation (WTW), the heat in this system can be extracted from the warm air inside and added to the cold air from outside, which is thus preheated. This system is called balanced ventilation.
Many consumers are critical about balanced ventilation in homes and air treatment systems in utility buildings. However, heat recovery systems exist that are incorporated into radiators and that do not suffer from the same drawbacks as central heat recovery systems. These systems do not require air ducts.