Free Area Louver Calculation

Determine the effective free area of a louver based on its dimensions, blade configuration, and frame. Free area is crucial for ventilation system design, ensuring adequate airflow while providing weather protection or visual screening.

Enter your louver specifications below and click “Calculate Free Area”.

Louver Dimensions & Specifications
Units for all dimensions:
Overall Louver Width (W):		in
Overall Louver Height (H):		in
Number of Blades (N):		blades
Effective Blade Thickness/Blockage (Beff): (Vertical height blocked by one blade)		in
Frame Thickness – Sides (Fs): (Thickness of one side frame member)		in
Frame Thickness – Top & Bottom (Ft): (Thickness of one top/bottom frame member)		in
Note: This calculator assumes standard rectangular louvers with evenly spaced, parallel blades. Effective Blade Thickness/Blockage should account for the actual material thickness and its angle relative to airflow.

Understanding Louver Free Area

The “free area” of a louver is the total open space available for air to pass through. It’s a critical parameter in designing ventilation systems, as it directly impacts airflow rates and pressure drop across the louver. A higher free area generally means less resistance to airflow.

Manufacturers typically provide free area data, but it can also be estimated. The calculation involves subtracting the area occupied by the frame and the blades from the louver’s total face area.

Simplified Calculation Approach:

A common method to estimate free area is:

1. Calculate Internal Width (W_int): Overall Width (W) – 2 × Side Frame Thickness (Fs)
2. Calculate Internal Height (H_int): Overall Height (H) – 2 × Top/Bottom Frame Thickness (Ft)
3. Calculate Total Blade Blockage (B_total): Number of Blades (N) × Effective Blade Blockage (B_eff)
4. Calculate Open Vertical Height (H_open): Internal Height (H_int) – Total Blade Blockage (B_total)
5. Calculate Free Area (A_free): Internal Width (W_int) × Open Vertical Height (H_open)
6. Calculate Free Area Percentage: (A_free / (W × H)) × 100%

This calculator uses this approach. Ensure all input dimensions are consistent (e.g., all in inches or all in millimeters). The “Effective Blade Blockage” is key; it’s not just the material thickness but how much vertical space each blade effectively obstructs due to its angle and profile when viewed head-on.

Why is Free Area Important?

• Airflow Performance: Directly influences the volume of air that can pass through the louver at a given pressure. Essential for HVAC intake/exhaust, generator room ventilation, etc.
• Pressure Drop: Louvers create resistance to airflow (pressure drop). Higher free area usually means lower pressure drop, reducing fan energy consumption.
• System Sizing: Engineers use free area to select appropriately sized louvers to meet required airflow rates for building ventilation or equipment cooling.
• Weather Protection: While maximizing free area is good for airflow, louver design also considers weather resistance (e.g., rain, snow). This often involves a trade-off; more weather protection might mean less free area.

Further Reading & Resources

AMCA International ASHRAE CIBSE (UK) Understanding Louver Free Area (Greenheck)