How Many Exhaust Fans Does a Factory Need?

One of the questions we often receive is:

“How many exhaust fans do I need for my factory?”

There is no fixed number. The first step is to calculate the workshop volume and then estimate the required airflow based on the air change rate.

For general industrial workshops in China, around 6 air changes per hour (ACH) is often used as a starting point for preliminary ventilation calculation. The actual requirement can be higher if the workshop has heavy heat loads, smoke, dust or other pollutants.

A Simple Example

Suppose a workshop is:

• 60 m long
• 30 m wide
• 6 m high

The workshop volume is:

60 × 30 × 6 = 10,800 m³

If we use 6 air changes per hour:

10,800 × 6 = 64,800 m³/h

So the workshop needs about 64,800 m³/h of exhaust airflow.

If one exhaust fan can provide an effective airflow of about 36,000 m³/h, then:

64,800 ÷ 36,000 = 1.8

In this case, 2 exhaust fans would be a reasonable starting point.

Fan Airflow Is Not the Only Factor

In real projects, we do not select the fan quantity only by dividing the required airflow by the rated fan airflow.

The final result can also be affected by:

• Air inlet size
• Louvers and safety guards
• Workshop layout
• Large machines or partitions
• Fan installation position

If fresh air cannot enter the workshop easily, the actual exhaust airflow will be lower.

A better arrangement is usually to place the exhaust fans on one side of the building and leave enough air inlets on the opposite side.

The airflow path should be:

Fresh air → Working area → Heat and stale air → Exhaust fan → Outside

What Information Do We Need?

For a basic factory ventilation calculation, we normally ask for:

• Workshop length, width and height
• Main production process
• Main heat sources
• Whether there is dust, smoke, oil mist or corrosive gas
• Possible fan installation positions

With this information, we can estimate the required airflow and recommend a suitable number of industrial exhaust fans.

For workshops with heavy heat, welding fumes, dust or chemical gases, the ventilation system should be designed according to the actual working conditions rather than using a simple ACH calculation alone.

Example summary:
Workshop size: 60 × 30 × 6 m
Workshop volume: 10,800 m³
Reference air change rate: 6 ACH
Required airflow: 64,800 m³/h
Fan airflow: 36,000 m³/h each
Recommended starting quantity: 2 fans