A ventilation system is a system which circulates fresh air throughout a confined space or spaces, while removing contaminated or stale air. Ventilation systems are used in various settings, including homes and workplaces. The many uses of these systems may include maintaining a constant humidity and temperature, ridding the air of dust and allergens, and providing the proper exchange of oxygen and carbon dioxide levels.

There are various types of ventilation systems, which are typically classified as natural or mechanical systems. A natural ventilation system relies on atmospheric conditions, while a mechanical system is a man-made device that assists in the filtration and circulation of the air. The most common form of a natural system consists of an outlet on the roof and openings throughout the lower part of a building. This allows air to rise and exit through the roof, and new air to enter from below, providing constant circulation.

Mechanical ventilation systems actively pull fresh air in and push old air out. They may have other capabilities, including heating and cooling, and require some form of energy to operate. One common form of mechanical ventilation system is the heating, ventilating, and air conditioning (HVAC) units which are used in homes and other buildings.

Advanced ventilation systems are used within certain industries as a safety measure. This kind of mechanical ventilation system may be required by law, depending on the industry. They are often required in mining, underwater, and majority of manufacturing industries.

The exact type of advanced mechanical ventilation system used will ultimately depend on the individual needs of the company and any applicable laws. Some of these industries may have to comply with stipulated air quality guidelines regarding requirements of such equipment. This may be dependent upon the geographical location of the particular facility. The main purpose of ventilation systems in such settings is to filter harmful substances from the air, provide a constant supply of oxygen, and maintain a healthy atmosphere for breathing.

A ventilation system can be used in conjunction with other equipment to establish desirable temperatures and to maximize the air circulation. It is not uncommon for large buildings and warehouses to be equipped with exhaust fans that assist in bringing in fresh air in while pushing the old out. These fans may be placed at various ventilation openings throughout the building or on the roof. A ventilation system with exhaust fans are often used in buildings that generate substantial amounts of heat or contain fumes.