Harold, I knew you would weigh in on this one! Thanks for your comments. I agree with everything you said. How do people set the humidistats on their attic fans? Or is it a bad idea to rely on a single humidistat in the attic for venting excess moisture in the winter?
Do you know if the garden variety humidistats make any compensation for temperature? For example, you know that attic air at 80 degrees and 50% relative humidity contains more water than air at 30 degrees and 60% relative humidity, and condensation of the warmer air may occur under the cold roof. Although the example is extreme, the setup with outdoor and indoor humidistats would not work in this case because the humidity in the attic is less than the humidity outside and the fan would not be turned on. Therefore condensdation may occur.