The basic difference between a supply fan and an exhaust fan is the direction in which they move air and how they affect pressure in a space. A supply fan pushes fresh air into a room, duct, tunnel or mine intake, creating a slight positive pressure inside. An exhaust fan pulls air out, creating a slight negative pressure that draws fresh air in through doors, windows, vents or intake shafts. Both are essential components of industrial and mining ventilation systems, and many installations use them together.
A supply fan is typically mounted so that its discharge is into the space or into a supply duct network. In industrial buildings it might be part of a make-up air unit, delivering filtered and sometimes heated or cooled air into a workshop. In mining, a main intake fan or an auxiliary forcing fan blowing into a duct is acting as a supply fan. Its role is to deliver enough clean air to dilute contaminants and control temperature and humidity. Because supply fans increase internal pressure slightly, they can help prevent dust or fumes from entering from adjacent dirty areas.
An exhaust fan is installed so that it extracts air from the space and discharges it outdoors or into a return airway. Examples include roof-mounted exhaust fans on factories, wall-mounted axial exhaust fans in workshops, and main exhaust fans on mine shafts that pull return air out of underground workings. Exhaust fans create a slight negative pressure in the area they serve, encouraging fresh air to flow in through designated intakes or openings. This is especially useful when the goal is to remove fumes, smoke or hot air from a space.
In many ventilation designs, supply and exhaust fans are used together in a balanced system. The supply fan delivers a known quantity of fresh air, and the exhaust fan removes a similar quantity of stale air. Balancing airflows prevents excessive positive or negative pressure, which could cause doors to slam, dust to be drawn in through cracks or conditioned air to leak out. In some systems, designers deliberately choose a slightly positive or negative balance to control where air enters or leaves.
From an equipment standpoint, the same axial or centrifugal fan design can often be used as either a supply or exhaust fan; the difference lies in how it is installed and ducted. What matters for performance is the required airflow and pressure, the nature of the air (clean, dusty, hot, explosive) and how the fan fits into the overall ventilation network.
In summary, a supply fan pushes fresh air in and tends to create positive pressure, while an exhaust fan pulls air out and tends to create negative pressure. Effective industrial and mining ventilation systems use both types in a coordinated way to control airflow patterns, contaminant levels and pressure differences.
