whole house fan
1. Don't ever turn on if downstairs windows/sliding glass doors are not open first. Minor implosion could crack sheet rock. (If putting in a switch in upper hallway, put it up high, away from small children.)
2. A multi speed unit is better if you can find it. Pay attention to sone levels. Balance unit. Sandwich in some foam as a shock absorber between rafters and fan.
3. Don't expect miracles. It works great to cool down house in early evening, 1 degree at a time, as daytime heat subsides. Won't help humidity/may make it worse. Then turn on A/C.
4. Also pulls in dirt and pollen. A filter won't work. Someone will dust more often (and complain/curse?).
5. Insulate/seal well in winter or cold attic air will get you.