The four types of ventilation are natural, mechanical, balanced, and exhaust. Natural ventilation is the process of air movement due to natural forces such as wind and temperature differences. Mechanical ventilation is the process of air movement due to fans, blowers, and other mechanical devices. Balanced ventilation is a combination of natural and mechanical ventilation, where air is both drawn in and exhausted. Exhaust ventilation is the process of removing air from a space, usually through a fan or blower. All four types of ventilation are important for maintaining healthy air quality in a space.