I live in a brick duplex with two stories, an attic, and basement (4 total) and the walk-up attic is finished down the center with crawl spaces on either side. There is no duct work in the attic and a gable window at the only outside wall. I don't think there's any insulation either. There was an ancient AC unit that I removed, and I only use it for storage. It gets very hot so I installed a gable fan (high powered meant for barns I think) right against the window. It's thermostatically controller and the window is open with a screen. I try to use it as a whole-house fan, and during cool days in the fall and spring I run it, open the door to the attic, and crack all the windows on the cool side of the house. I think this works pretty well but it is difficult to say if it works better or worse than just opening all the windows.
My question is one of general strategy. In the hot summer days when we run the air, should I leave this fan on or off? If on, at what temp setting? Also if on, should I leave the attic door in the upstairs hallway open or close? Will this help keep the attic, and therefore the whole house cooler while the ac is running, or will it suck all the conditioned air right out of the house? Please help, I get different answers from different AC guys I talk to who I think are just giving me "rule of thumb suggestions." Any advice is appreciated, and please let me know if I am missing some details that would help. Thanks! -KH