Abstract: An apparatus for ventilating the crawl space of a structure, comprising an exhaust fan adapted to at least partially occlude an aperture in a structure and oriented to, upon receiving an appropriate stumulus, exhaust crawl space air through said aperture to outside the structure, a temperature sensor and a relative humidity sensor for sensing the respective temperatures and relative humidities of crawl space air and of outside air, and for transmitting respective stimulus dependent thereon to a programmed computer, said computer determining the absolute moisture differential therebetween and comparing said differential to a pre-set minimum absolute moisture differential parameter for ventilation activation, said computer also functionally connected to said fan for controlling the activation thereof, said computer also programmed to discriminatorily activate either a humidity decreasing or a humidity increasing mode depending upon a maximum or minimum inside RH parameter, and to deactivate said mode at a break

Abstract: An apparatus for ventilating the crawl space of a structure, comprising an exhaust fan in a housing adapted to at least partially occlude an aperture in a foundation wall of a structure and oriented to, upon receiving an appropriate stumulus, exhaust crawl space air through said aperture to outside the structure, a temperature sensor and a relative humidity sensor for sensing the respective temperatures and relative humidities of crawl space air and of outside air, and for transmitting respective stimulus dependent thereon to a programmed computer, said computer also adjusting said relative humidity stimulii for temperature-dependent deviation, then determines the absolute moisture differential from said adjusted stimulii and compares said differential to a pre-set minimum absolute moisture differential parameter for ventilation activation, said computer also functionally connected to said fan for controlling the activation thereof