Louver Calculator
Size Intake/Exhaust or Check Capacity.
*500 FPM is standard limit for rain penetration.
Manufacturer Rating (Typ. 35-60%). Default: 50%.
In HVAC engineering, a Louver is a vent with angled blades that allows air to pass while blocking rain and debris. The most critical metric for a louver is its "Free Area"—the actual open space available for airflow after subtracting the obstruction caused by the frame and blades.
The Louver Free Area Calculator is an essential sizing tool for mechanical engineers. It helps ensure that intake and exhaust vents are large enough to handle the required Airflow (CFM) without exceeding velocity limits that would suck in rainwater.
Features
1. Check Capacity Mode: Input the physical dimensions () and typical efficiency (%) to calculate how much air (CFM) the louver can handle safely.
2. Size Louver Mode: Start with your required CFM (e.g., for a generator room) and find the minimum Face Area required.
3. Velocity Safety Check: Calculates the "Face Velocity." Standard industry practice is to keep this below 500 FPM (Feet Per Minute) to prevent water penetration. The tool flags high velocities.
4. Free Area %: Allows customization of the manufacturer's efficiency rating (typically 35-60%), which varies wildly between models.
5. Visual Diagram: Shows a schematic of the louver blades and airflow path.
Uses
- HVAC Design: Sizing fresh air intakes for buildings.
- Generator Rooms: Ensuring large diesel generators get enough cooling air/combustion air.
- Architectural: Calculating the visual size of vents needed on a building facade.
- Compliance: Meeting building codes that specify minimum "Free Area" for ventilation.
Tips
- The 50% Rule: A common rule of thumb is that a louver has 50% free area. However, heavy-duty storm louvers may drop to 35%, while simple stamped grilles can approach 60%. Always check the spec sheet.
- Water Penetration: The "500 FPM" rule is golden. If air moves faster than 500 ft/min through the intake, it will carry rain droplets with it, potentially damaging equipment inside.
- Face vs. Free: "Face Area" is the gross hole in the wall. "Free Area" is the net opening. Do not confuse them!
FAQs
What is CFM?
CFM stands for Cubic Feet per Minute. It is the volume of air moving through the louver.
Why do I need a calculator?
Because buying a 10 sq ft louver does not give you 10 sq ft of air. It might only give you 4 sq ft. If you undersize it, your fans will starve, motors will overheat, or walls may implode due to pressure.
What is FPM?
FPM is Feet Per Minute, measuring the speed (velocity) of the air. Velocity = Flow (CFM) / Area.
Final Words
Louver sizing is a balance between airflow and weather protection. This calculator ensures you strike that balance perfectly, keeping the fresh air flowing in and the rain staying out.
