fall, but it is useless in the middle of the summer. It is only useful when the temperature outside is lower than the inside, so even if you keep your house at 74 like we do, the temperature only goes lower than that at 1-2 am until 7 am. So you have to get up, open windows, and turn the fan on at 1 am, which just doesn't happen.

But, in the spring and fall, it cools the house down very well and brings in tons of fresh air with a nice breeze.