Technical Foundation
What Is a Intake Louver?
An intake louver is a fixed grille of angled blades set into a wall or equipment opening, admitting outside air for ventilation, combustion, or equipment cooling while excluding rain and physical intrusion. Blade geometry — the angle and depth of each slat — is engineered to intercept wind-driven rain before it reaches the free opening behind the louver, which is why louvers are rated by both free area (the effective open percentage available for airflow) and a wind-driven rain performance class.
Fixed-blade louvers are the standard, low-cost choice for continuous-flow applications like generator enclosures and equipment rooms, while adjustable and drainable-blade louvers add moving parts or built-in gutters to improve either airflow control or rain rejection at the cost of complexity. Free area, not the overall opening dimension, is the figure to size against the required airflow — two louvers of the same physical size can differ significantly in effective open area depending on blade design.
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| Spec | What It Means | Why It Matters |
|---|---|---|
| Blade Type | Fixed, adjustable (motorized/manual), drainable | Fixed is lowest cost; drainable improves rain rejection; adjustable adds airflow control |
| Free Area | Typically 40-60% of overall opening | The actual figure to size against required CFM, not the overall louver dimension |
| Frame Material | Extruded aluminum, mill or painted finish | Aluminum resists corrosion in outdoor wall-mounted service |
| Screen Option | Bird screen, insect screen | Prevents pest and debris intrusion while adding a small further reduction in free area |
| Wind-Driven Rain Class | Manufacturer-rated performance class | Determines how much water penetrates the louver under a given wind speed and rainfall rate |
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Applications
Where Intake Louvers Get Used
Intake louvers are specified anywhere outside air must enter a wall or enclosure opening while excluding wind-driven rain and debris.
HVAC Mechanical Rooms
Intake louvers supplying outside makeup air to rooftop and mechanical room HVAC equipment.
Generator & Equipment Enclosures
Fixed and drainable blade louvers providing combustion and cooling air intake for standby generator enclosures.
Data Center & Electrical Room Ventilation
Louvers sized for high free area to support heat rejection airflow in equipment-dense spaces.
Industrial Building Ventilation
Wall-mounted intake louvers supplying general ventilation air to plant and warehouse buildings.
Parking Garage & Stairwell Pressurization
Code-required intake louvers providing combustion and pressurization air per building ventilation requirements.
FAQ
Intake Louvers Questions, Answered
What's the difference between free area and overall louver size?
Overall size is the physical opening dimension the louver frame fills, while free area is the percentage of that opening actually available for airflow after accounting for the blades, frame and any screen — typically 40-60% of the overall opening. Airflow calculations must use free area, since sizing against overall dimension will significantly undersize the required louver for a given CFM.
When do I need a drainable blade louver instead of a standard fixed blade?
Drainable blade louvers include a built-in gutter system in each blade that channels intercepted rainwater to the sides and out of the louver rather than letting it drip through to the space behind. They're specified where higher wind-driven rain performance is needed — coastal locations, tall buildings with high wind exposure, or any opening protecting moisture-sensitive equipment.
Do I need a bird screen or insect screen on my intake louver?
Most outdoor intake louvers include a bird screen as standard to prevent nesting and pest intrusion; insect screen is added where finer mesh is needed but further reduces free area and increases pressure drop, so it's typically specified only where fine debris exclusion is a real concern, such as filtered equipment intakes.
How is a louver's free area affected by adding a screen?
Each added screen layer reduces the louver's effective free area, sometimes significantly for finer insect mesh, so a louver's free area rating with a screen installed can differ meaningfully from its bare-blade rating. Confirm the free area figure quoted already accounts for whatever screen option is included.
What wind-driven rain class should I specify?
Wind-driven rain class should match the exposure and sensitivity of what's behind the louver — a higher class is warranted for coastal or high-wind locations, or where the space behind houses moisture-sensitive electrical or mechanical equipment. Manufacturers publish rain penetration performance data at specified wind speeds and rainfall rates for each class.
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