What is Louver Free Area?

It's the available open area of a louver with removing the blades, frame, and stiffeners. AMCA publication 500-L prescribes the method for determining louver free area.

Note: Most often, the louver spec calls for 50% free area, but the size of the louver makes a big difference in the free area. For example, a 48” x 48” AMCA tested louver may have a 50% free area, but the same louver in a much smaller size may only have 30% free area and the opposite for larger assemblies could have more than 60% free area.

So, specifying a louver on its 48” x 48” free area size is not recommended.