How to calculate the size of a ventilation fan for a factory with a height of 6 meters, simple and practical.

How to calculate the size of a ventilation fan for a factory with a height of 6 meters, simple and practical.

Complete with examples of calculations that factory engineers commonly use.

✅ 1) The most commonly used basic calculation method.
A. Calculated from the number of Air Changes per Hour (ACH).
Standard formula for general factories (General Ventilation):
CFM = (area × height × ACH) / 60
m³/hr = Area × Height × ACH

ACH value according to factory characteristicsArea Type Recommended ACH Value
Warehouse 6–10 ACH
General work / product packing 10–15 ACH
The work is hot 15–20 ACH
Some smell/smoke work 20–30 ACH
Very hot work / welding work 30–50 ACH

✅ 2) Example of calculating a fan for a factory with a height of 6 meters.Assume the following information:
 • Factory area = 20 × 40 m = 800 m²
 • Height = 6 m
 • General job type → Select ACH = 12.

✨ Calculation steps
1) Find the volume of the building.
Volume = Area × Height = 800 × 6 = 4,800 m³

2) Find the total ventilation rate.
Airflow (m³/hr) = Volume × ACH
= 4,800 × 12
= 57,600 m³/hr

Convert to CFM (if desired)
1 m³/hr = 0.5886 CFM → 57,600 × 0.5886 = 33,888 CFM

✅ 3) Select the number of fans.If using a farm fan of
 • 30 inches = ~14,000–16,000 m³/hr
 • 36 inches = ~18,000–22,000 m³/hr
Choose average 20,000 m³/hr per machine.
Need a fan = 57,600 ÷ 20,000 ≈ 2.88 → round to 3.
📌 Summary: Factory 800 m² high 6 m uses about 3 farm fans.

✅ 4) Principles for effective fan placement
✔ Negative Pressure placement
 • One wall mounted fan.
 • The other side is the air inlet (Fresh air louver).
 • One-way air flow → pulls out exhaust air well.

✔ Installed approximately 1.5–2.0 m from the floor.To pull the hot air that floats upwards better.
If the work is very hot May add a fan on a high level (High mount)
✔ Do not place fans facing each other.The wind will swirl and the actual amount of wind will decrease.

✅ 5) In the case of very hot work (e.g. furnace, heat treatment)
Introducing the Heat Load Method calculation method.
Airflow (m³/hr) = Qₕ (kW) × 3,000
For example, heat 50 kW → wind required 150,000 m³/hr.
(Must use several or use Roof Fan + Side Fan mixed together)