As with any conditioned environment a relative low humidity and maintained temperature between 74 to 80 degrees is recommended.  We are addressing several factors, most importantly is the proper operation of the back draft damper. Our patented design prevents exterior air from entering and mixing with conditioned interior air which would and does provide the right conditions for mold development in and around the bathroom exhaust fan.  In addition, this prevents corrosion in the dryer duct and assembly. 

Eliminates water / sand intrusion

We recommend using our box along with proper construction sealant (Sika Flex, Dymeric 112 are suitable) installed in a properly sized rough opening directly on the CMU or PIP surface.  Regarding “Eliminates water intrusion” we are implying that with proper installation water will not enter the building at the box location.  We have a monolithic box cavity design which eliminates the seam between the box cavity and the louver.  This has and continues to be a direct source of water intrusion and also contributes to mold and mildew.