Louver free area calculator
Louver free area calculator.
Free area is the open part of a louver’s face that air passes through. Enter the size and the free-area percentage published for the model to see the free area, how a wide louver is built in sections, and the size you need for a required free area.
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Louver free area calculator
Size for a required free area
What free area means
A louver’s face includes its frame and blades, so only part of it is open. Manufacturers publish free area for each model, as square feet at a test size or as a percentage of the face. The percentage changes with size, so use the figure for a size close to yours.
Face area and billing
Price books charge louvers by the face area in square feet, often with a minimum for small units. The calculator shows the face area and, when you enter a minimum, the area that is billed.
Sections and mullions
A louver wider than a model’s largest section is built in equal sections joined by mullions: a 12'-6" louver with a 5'-0" section limit is three sections of 4'-2" with two mullions.
Sizing for airflow
The mechanical engineer usually states the free area a louver must provide. Divide it by the free-area fraction to get the face area, then by the height to get the width. Check the result against the model’s published free area and pressure drop.
Common questions
How is louver free area calculated?
Face area (width × height ÷ 144, in square feet) × the free-area percentage published for the model. A 12'-6" × 6'-0" louver at 55% has 75 sq ft of face and 41.25 sq ft of free area.
Why is free area lower on a small louver?
The frame takes a larger share of a small face, so the open percentage drops. Use the manufacturer’s figure for your size.
See it with your own data.
Start with one spreadsheet and a result you already know.