Commonly used methods for the treatment of harmful gases in ventilation systems include absorption adsorption. Absorption method is to utilize appropriate liquid as absorbent to contact with the air containing harmful gases, so that the harmful gases are absorbed by the absorbent chemically react with the absorbent become harmless substances. Adsorption method is to use certain substances with large adsorption capacity as adsorbents to adsorb harmful gases. Activated carbon is the most widely used adsorbent in industry. The adsorption method is suitable for the treatment of hazardous low concentration of harmful gases, the adsorption efficiency can be close to 100%. Because of the lack of economic effective treatment methods for certain harmful gases, high chimneys can be used as a last resort to discharge untreated incompletely treated air into the air. This method is known as high altitude emissions. Air Heater In areas with very cold winters, cold outdoor air cannot be sent directly into the room, but must be heated. Usually a surface heat exchanger is used to heat the air with hot water steam as the heat medium.