This scenario illustrates a basement/crawl space combination in which the Humidex is installed in the basement. Note that the Humidex is installed at the entrance footing of the crawl space to permit both areas to draw replenishment air, via floor grill for the crawl, and stairs for the basement. In rare circumstances some homes may encounter crawl space air infiltrating through the floor register and push musty air upstairs. This can be treated by installing a booster fan system in the crawl space floor register. The crawl space replenishment air then becomes mechanically drawn instead of passive, and eliminates any chances of crawl space air migrating upstairs. One other option is to install a crawls space model in addition to the basement model, then servicing both areas independently and eliminating replenishment air issues.