No louver may be considered 100% waterproof or stormproof. Depending on the louver type, application and configuration Greenheck recommends sizing conventional intake louvers at or around 75% of the products capacity with the capacity defined as the “Beginning Point of Water Penetration”. As an example, Greenheck model ESD-635 has a Beginning Point of Water Penetration of 1077 FPM free area intake velocity. Greenheck recommends sizing model ESD-635 around 800 FPM for intake applications to reduce the likelihood of nuisance weather infiltration during ambient weather conditions. Regardless of how conservatively or aggressively the louvers are sized Greenheck always recommends provisions to manage water infiltration.