It facilitates the drying up of moist or moist parts in the sub-floor area because dry air is constantly being blown in excess of them. It is actually more practical than wanting to power out the moist air within the damp surfaces. Sub floor ventilation followers reduce mould and mildew http://commercialelectricalcontr42932.thezenweb.com/What-Does-Sub-Floor-Ventilation-Mean--23374120