The damp air exhausted by the Humidex must be replaced by the warmer/drier air from the upper levels. If there is no open stairwell, the airflow is restricted from coming down; then install a passive return grille with 100 sq. inches either in the door, in the wall, or in the floor to allow unobstructed air downstairs.
 |  |
When the flow is limited or inaccessible between rooms downstairs (if there are walls or partitions), then install a grille 8” x 10” (or other grill configuration, having total area of not less than 80 sq. in.) in the bottom of the door or wall to avoid having stagnant air in those areas. Otherwise, interior doors must remain open. This ensures that all the air drawn into the Humidex comes from all areas of the basement.
In the initial period after installation, before the Humidex has had time to dry out the basement, and when the air outside is hot and humid; keep the basement/crawlspace doors, windows and vents closed to the outside. This will assure that the air is replenished with the air from upstairs and not with the humid air from outside. Generally, for improved performance, it is best to keep all exterior basement/crawlspace doors, windows and vents closed at all times.
Please check to make sure there are no openings/leaks around windows, doors, vents or other places, where outside humid air can enter the basement/crawlspace. Make sure that A/C Ducts are properly sealed and that all A/C Leads to the basement are closed. Sump Pumps holes should be properly covered.
Note: When a Mechanical Booster Fan is used to provide replenishment air, the unit should have a max capacity of 150 CFM.
