Louver Calculator
Size Intake/Exhaust or Check Capacity.
*500 FPM is standard limit for rain penetration.
Manufacturer Rating (Typ. 35-60%). Default: 50%.
In buildings, factories, and HVAC systems, louvers are used to control airflow while protecting openings from rain, debris, and direct sunlight. You can see them on walls, rooftops, doors, and ventilation panels. While a louver may look like a large opening, not all of that space actually allows air to pass through. The blades, frames, and supports block part of the opening.
This is why engineers and designers focus on something called free area. Free area is the portion of the louver that is truly open for air to flow. A Louver Free Area Calculator helps you find this value quickly and accurately.
In this guide, you will learn what free area means, how the calculator works, the formulas it uses, and how to apply the results in real ventilation projects.
What the Louver Free Area Calculator Is
A Louver Free Area Calculator is an online tool that calculates the effective open area of a louver. It subtracts the space blocked by blades, frames, and other parts from the total opening size.
The calculator helps you determine:
-
Actual airflow opening size
-
Free area percentage
-
Whether a louver meets ventilation requirements
This tool is widely used in:
-
HVAC system design
-
Building ventilation planning
-
Industrial exhaust systems
-
Architectural projects
Instead of estimating by eye, you get precise numbers for better airflow performance.
How the Louver Free Area Calculator Works
Inputs You Enter
Most louver free area calculators ask for:
-
Louver width
-
Louver height
-
Blade width
-
Number of blades
-
Frame or support obstruction size
Some tools may also allow airflow-based inputs like CFM and face velocity.
Calculation Process
The calculator:
-
Finds the total louver opening area
-
Subtracts the blocked blade and frame areas
-
Calculates the free area
-
Computes the free area percentage
Output You Get
You receive:
-
Free area (open space for air)
-
Free area percentage
These results help you decide if the louver is suitable for your ventilation needs.
Key Formulas Used
Total Louver Area
A_{total} = Width \times HeightObstructed Area
A_{blocked} = Blade\ Area + Frame\ AreaFree Area
A_{free} = A_{total} - A_{blocked}Free Area Percentage
FreeArea% = \frac{A_{free}}{A_{total}} \times 100Airflow-Based Estimation (Optional)
A_{free} = \frac{Airflow}{Face\ Velocity}These formulas help convert physical dimensions into useful airflow values.
Step-by-Step Examples
Example 1: Basic Louver Opening
Suppose a louver has:
-
Width = 1.2 m
-
Height = 1.0 m
Total area:
A_{total} = 1.2 \times 1.0 = 1.2 \text{ m}^2If blades and frame block 0.4 m²:
A_{free} = 1.2 - 0.4 = 0.8 \text{ m}^2Free area percentage:
FreeArea% = \frac{0.8}{1.2} \times 100 = 66.7%So, only 66.7% of the opening allows airflow.
Example 2: HVAC Airflow Requirement
If an HVAC system needs 2000 CFM and face velocity is 500 ft/min:
A_{free} = \frac{2000}{500} = 4 \text{ ft}^2The louver must provide at least 4 square feet of free area.
Features of the Louver Free Area Calculator
Accurate Obstruction Handling
The calculator accounts for blade and frame blockage.
Free Area Percentage
You can see how efficient the louver opening really is.
HVAC Friendly
Useful for airflow and ventilation sizing.
Fast Results
No manual math needed.
Beginner Friendly
Simple inputs, clear outputs.
Uses and Applications
HVAC System Design
Engineers use free area to ensure enough air enters and exits the building.
Industrial Ventilation
Factories need proper airflow for safety and cooling.
Building Codes
Many codes require minimum free area values.
Architectural Planning
Designers choose louvers that balance airflow and appearance.
Equipment Cooling
Machines need proper ventilation to avoid overheating.
Helpful Tips for Best Results
Measure Blade Thickness Correctly
Thicker blades reduce free area.
Consider Rain and Sand Louvers
Weather protection louvers usually have lower free area.
Check Manufacturer Data
Some provide exact free area percentages.
Match Airflow Needs
Always size louvers based on required CFM.
Leave Safety Margin
Extra free area improves performance.
Common Mistakes to Avoid
Using Total Area Instead of Free Area
Air does not pass through blocked sections.
Ignoring Blade Overlap
Overlapping blades reduce airflow.
Wrong Units
Keep all measurements consistent.
Underestimating Obstructions
Frames and supports also block air.
Forgetting Velocity Limits
High velocity causes noise and pressure loss.
Frequently Asked Questions
What Is Louver Free Area?
It is the open space where air can flow.
Why Is Free Area Important?
It affects airflow and ventilation efficiency.
Do All Louvers Have the Same Free Area?
No, blade design changes it.
Can This Be Used for Exhaust Systems?
Yes, for both intake and exhaust.
Is Free Area the Same as Opening Size?
No, it is always smaller.
Final Words
The Louver Free Area Calculator is an essential tool for anyone working with ventilation, HVAC, or building design. It helps you understand how much air can actually pass through a louver, not just how big the opening looks.
By using correct measurements and reliable formulas, you can select the right louvers, improve airflow performance, and avoid costly design mistakes. Whether you are planning a small building or a large industrial system, this calculator gives you the clarity you need for efficient and safe ventilation.