First, understand what balanced ventilation is:

Large boilers adopt balanced ventilation, which means that both the supply fan and the induced draft fan are installed in the boiler flue gas and air system. Using a blower to overcome the resistance of the air duct and burner, and sending air into the furnace to make the air duct work under positive pressure; Utilize induced draft fans to overcome the resistance of all flue ducts, heating surfaces, and desulfurization and dust removal equipment, enabling the furnace and flue ducts to operate under negative pressure. Balanced ventilation can effectively supply air and exhaust smoke, while also maintaining a reasonable negative pressure for the furnace and flue. Compared to positive pressure ventilation, it ensures the safety and hygiene of the boiler room; Compared to negative pressure ventilation, the air leakage is smaller. So large and medium-sized boilers adopt balanced ventilation.

In order to prevent flames and high-temperature smoke from spraying out and injuring people, and to avoid environmental pollution, negative pressure is used in the furnace. During normal operation of the boiler, the furnace usually maintains a negative pressure of -40 to -60 Pa. Excessive negative pressure can cause an increase in cold air leaking into the boiler from the outside, resulting in an increase in exhaust gas temperature and a decrease in boiler thermal efficiency.