1) Duct Fan: The Duct fan works by reducing the pressure of the environment. In air conditioning, it is necessary in systems that work with indoor and outdoor air mixture. Duct fans ensure that the air in the air conditioned environment is returned in an appropriate amount. In systems with surplus pressure, Duct fans operate at a lower flow rate than discharge fans.

2) Exhaust Fan: Exhaust fan is used in systems that work with internal-external air mixture but without duct fan and provides exhaust air as much as intake air. In these systems, the discharge fan must be selected to meet the static pressure generated in the system in the absence of outside air. In the case of outside air, the exhaust fan ejects a slightly lower amount of return air than the intake air, thereby creating a surplus pressure in the space.

3) Discharge Fan: The fan connected to an air duct creates surplus pressure within the duct and provides air movement. This type of fans are called discharge fans.