Calculating Louver size for Fresh Air Intake

Article details

Calculating the size of the Louver for Fresh Air Intake requires consideration of both The required air volume (CFM) and the air speed passing through the Louver (Face Velocity) in order to get the appropriate Louver cross-section size without making loud noise. Does not absorb rainwater and work efficiently

✅ 1. Louver size calculation formula

\text{Area}_{\text{Louver}} = \frac{\text{Airflow (CFM)}}{\text{Face Velocity (fpm)}}
 • Airflow (CFM) = Air volume required to pass through the Louver (cubic feet/minute).
 • Face Velocity (fpm) = Air velocity in front of the Louver (Usually use 300–500 fpm for Fresh Air)

✅ 2. Standard value that is commonly used.

Recommended Face Velocity Usage Type (fpm)
Fresh Air Intake 300–500
Exhaust Air 500–800

✅ 3. Example calculation

Problem: Want air to enter the building. 2,000 CFM via Louver
 • Use Face Velocity = 400 fpm.
\text{Area}_{\text{Louver}} = \frac{2000}{400} = 5 \text{ ft²}

Therefore, you need a Louver size 5 square feet (not including Free Area Correction).

✅ 4. Adjusting size from Free Area (actual opening)

Louver has an average free area of 45–60%.
The Free Area must be divided to get the actual size of the Louver:

\text{Required Area}_{\text{Actual}} = \frac{5}{0.5} = 10 \text{ ft²}
 • If Free Area = 50% is selected → Louver size 10 ft² must be used.

✅ 5. Summary of calculation steps.
 1. Calculate the CFM required to receive wind.
 2. Select the appropriate Face Velocity (e.g. 400 fpm).
 3. Calculate Area = CFM ÷ Face Velocity
 4. Adjust with Free Area → Area ÷ Free Area (%)
 5. Design the frame size such as width × height (such as 2’ × 5’ = 10 ft²).

✅ 6. Example of actual size.

want to add air 2,000 CFM with Louver at Face Velocity = 400 fpm and Free Area 50%:
 • Louver total size 10 ft² required.
 • May choose to use Louver size 2.5 ft. × 4 ft. (10 ft²).
 • Make sure that The installation location is not directly exposed to rain and has a Drainage/Drip Edge.