Louver Free Area

Free area - the sum of the areas of the minimum gap between two louvers through which air passes.

Note:

When measuring two louvers placed back to back, the free area for the combined louvers shall be determined as the smaller of the two free areas.

Horizontal blade louvers

A = Minimum distance between the head and top blade.*

 Note: Where the top blade dimension C is less than A, use the value for C. B = Minimum distance between the sill and bottom blade.*

C = Minimum distance between adjacent blades. Note that in louver Type 2, C may not be equal to C1.*

N = Number of C openings in the louver.

L = Minimum distance between louver jambs.

W = Actual louver width.

H = Actual louver height.

* The A, B & C spaces shall be measured within one inch from each jamb and averaged.

Vertical blade louvers

A* = Minimum distance between the left jamb and left blade.*

 Note: Where the left blade dimension C is less than A, use the value for C. B* = Minimum distance between the right jamb and right blade.*

C* = Minimum distance between adjacent blades.*

N = Number of C openings in the louver.

L = Minimum distance between louver head and sill.

W = Actual louver width.

H = Actual louver height.

* The A, B & C spaces shall be measured within one inch from each blade end and averaged.