Attic fans are a waste of money. I had looked into getting one a few years ago on the idea that it seemed to make surface that cooling the attic would cool the house. But while that sounds good on the surface, it doesn't make any sense. If the attic is well insulated, then it doesn't matter how hot it gets. In most cases, from what I've read, attic fans end up sucking the cooler air from the upper level of the home into the attic (via openings in vents, cracks and so on). The ideal would be that the fan sucks in air from under the eaves, assuming vents aren't blocked by insulation as they are in many cases. But the again, if your attic is well insulated, cooling it doesn't have any impact on the living area below it.
Some gov't agency (EPA?) has done studies that are pretty conclusive that attic fans use more energy than they save. Plus the sucker was noisy and you could feel the vibrations upstairs, so we had stopped using it anyway. I think those passive whirlygig things are probably a much better idea, everyone in Dallas had those.
We could have added vents just above the gutters, that would have provided a steady convection flow but it was going to be relatively costly and require cutting across the plywood and weakening the structure just a bit. We won't be in the house long enough to justify that.
