If you use a whole house fan, there is no point in having a sealed attic system. You need an old fashioned "open" attic system. You want the hot air to vent out through the gable ends. You have a grate in a hallway that opens and the (presumably) cooler air from outside the home is drawn in through the open windows through the home, through the grate, and exits through the attic vents. WHole house fans are NOT compatible with conjunctively using your AC system. And, as I mentioned, the exterior of the home must be cooler (and less humid) than the interior for the whole house fan to be a viable option. 85° is pretty hot for most people, and I presume you're in the South where the humidity is also very high. Southerners LOVE their AC for a reason and long ago abandoned their whole house fans except for about 15 days in the spring and fall. WHole house fans are like owning a convertable. It sounds like a good idea, and if you live in a place like San Francisco, it probably IS a good idea. But, for folks who live in most of the rest of the country, there just isn't enough ideal weather in the year to be able to fully utilize that top down motoring.

We had a similar need, but only because I did not want the hassle or visibility of cutting into the ceiling to install a whole house fan. what I came up with after much searching has been a PERECT solution for us. It is a window mounted whole house fan. I did not have any thought that it would actually move air in the same quantity as the conventional whole house can. It is MARVELOUS! I am pasting the url for the site from which I ordered ours.It has been two years now and I would never be without it again. They install in any conventional window of reasonable size (see site instructions), and attach only by 4 little screws into the inside of the facing and do not show. They have switches that can be turned to either sucking or blowing so you can vary the pull either way. The window can shut down behind the fan for rain or winter. And it draws air in a major way. We have saved scads on electricity bu using it when the nights are cool enough to leave it on all night and then close up in the day. The AC will not come on for hours or even at all, of course depending on how cool it got and how hot it reaches in the day. We love VERY cool air so can tolerate it getting down to 62 or so at night to keep it from getting very hot the next day. That would all be determined by your own tastes.... They were out of stock when I ordered and so I had to wait a couple of weeks, but the company shipped promptly once they had them in stock. I am so glad we went that route! Check it out. Here is the url: http://www.rewci.com/20wholhouswi.html

All that advice and no mention of existing attic ventilation??? What gos in must go out. Translated means that unless you have far more square inches of attic vents than normal,a ceiling installed fan will perform poorly. You might even create health hazzards if the attic has insufficent exhust vents. The fan creates a high postive pressure in the attic and negative pressure inside living area. Air leaking back into living area will be heavly contaminated with dust,insulation particals and possibly worse. The conventional method of overcoming this is large movable shutters in one or more gables. Your origional plan of mounting fan in gable completly eleminates issues of pushing dirty attic air into living area.

There are a number of solutions when it come's to whole house fans. My fav is gable mounted,axial flow if space premits,centrifugal in crowded quarters. In a large floor space such as yours mecanicaly opened shutters in ceiling and mechanicalll closed in oppisite gable are sometimes required.