My only knowledge is with a whole house fan, not with a roof mounted attic fan. So my experience may be of No benefit to you. My BIL had one installed in his house on Moultonborough Neck Road, in the ceiling of the hallway at the 2nd floor landing. It was the whole house type with the automatic louvers and belt driven motor, approx. 3' sq. His only exhausted into the attic and not directly to the outside.
It worked so well that in the late afternoon / evening as the sun would be going down, he could turn on the fan and open ANY window in the house, even just a few inches, (we experimented) and you could instantly feel a breeze moving through the house. The more you opened a window or windows the bigger the breeze would get. I was pretty impressed.
I am sure some of it's great performance was due to it's location, the layout of the house etc. When he built his house, the fan was part of his overall plan, so there was adequate ventilation added so that all this extra air could then escape the attic via ridge and gable vents
So, due to that experience alone, I think "Whole house Fan" are a great idea.
Given the amount of air one of the fans can move I can't imagine how a roof mounted exhaust fan wouldn't work well in cooling an attic, as long as it can pull adequate cooler or fresh air from either outside or through the house itself.
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