I live in Nashville, where it's quite humid. I moved into my first house last August and we have a stand-up crawlspace. Around the exterior of the crawlspace, the builder put in four vents. About a month after moving in, we started to see what looked like mildew and/or mold growing on the walls of the crawlspace. I had a "mold guy" come in and he recommended a dehumidifier. I had a friend of mine who knows quite a bit about DIY stuff come to my house and he recommended getting a humidistat fan instead. Before I rush out and buy one and put one in, what do I need to know about using humidistat fans? Are there certain factors that make them uneffective that I need to be aware of?