Does it matter which direction the louvers face on rectangular undereave vents when they are installed?

No, it does not matter which direction the louvers face on rectangular undereave vents when they are installed.

No, it does not matter. The direction the louvers face does not affect the rectangular undereave vent's performance (airflow or weather protection) at all. In fact, as a point of comparison, Air Vent also makes continuous soffit vents in 8-foot lengths that include louvers facing one direction and louvers facing the other direction alternating within the same 8-foot length. Air Vent does not specify which direction the louvers should face because it does not matter.