Note the volume of air flow from the smoke pen as the HVAC system is entergized. The home was noted with loosened duct connections and open bottom board causing a lost of supply air to the outside of the home. The balance of return air, that lost to balance the supply, is drawn through air infiltration voids.
This video is also related to another video on this site that depicts the rainwater entering the skirting material, thus the moisture trail into the wall cavity and home via air infiltration points.
See how drainage under home can lead to the interior HVAC unit "wicking" moisture back into air handler cabinet for redistributiion through home - the resultant concern .......