There has been a whole house fan between the second floor and attic of my house for some time. We usually have it on with the downstairs windows open. I just had a thought: Should there be an open outlet/vent to outside when the fan is on? Can I get a remote opening one, so I don't have to go all the way up there when I turn it on? It does pull very strongly as it is, but would adding a vent cause a notable difference?
The concept of a whole house fan is two fold. One is to bring in the cool evening air, the second is to flush out the hot air that is trapped in the attic. Your attic should already be vented enough to allow the incoming air a place to push the hot air out. If you where to make an opening for the fan to vent it, the cool air will just travel straight to it and not cool the attic as well.