Whole-house fans are designed to cool the whole house. Typically, they pull air from the outside and vent it into the attic. I have one, and it is on right now. I have some of strategically opened windows around the home, opened just a crack, and the fan is doing a good job of drawing in the cooler outside air in, and pushing the hot air into the attic, through the eve vents, and eventually outside. The result is a cooler home and attic, cheaper to run than the a/c.

Of course, it is 2:30 am, and the outside air is much cooler than the house, which has been absorbing heat all day. Although I have tried various window combinations with the whole-house fan during the day, it just does not work the same as the a/c. It does cool off the attic some, but my attic is an attic, not a room. I do not believe a whole-house fan will work for you because it is designed to work with a fully breathing normal attic. Your problem could be that there is no insulation in the attic walls, or something else wrong with its design. A couple of questions:

How old is your house? Are the walls and ceilings insulated? Does it appear that the drywall/plaster ceilings match the contour and slope of the roof? Any other information you may have might be helpful as well, and I might be able to offer a suggestion.

Thanks - TomR

I have had a $150 whole house fan sitting in the garage now for two years.

Why? Beacuse our old house doen't have anywhere near the required exhaust vents. A 36" whole house fan needs about 16 of those little roof vents you've probably never noticed on your roof.

Check your math for the fan before you consider one of these promising goliaths.

Yep, same problem with my fan. I only had small gable vents. When I turned the fan up to full speed, it would start shaking and rattling. If I opened one of the attic doors, this wall of hot air would rush into the room, and the shaking and rattling would stop.

I added a ridge vent, which improved the situation, but did not completely solve it. I may add a couple of other roof vents this fall.

Still, the whole-house-fan relies on the ease of air moving around in the attic for proper venting and cooling. In your case, the attic is a room, and the flow of air would be restricted since there is probably no direct air access any more to whatever roof/gable vents you have. This is a common problem with attic-to-room conversions when the need for the original attic to breathe is not taken into consideration, and built into the addition.

Oppposite problem here. I have the whole house fan installed. It vents okay but the heat here is extreme (over 100). When I cool the house using AC, I get moisture dripping from the tops of the walls surrounding the hall where the fan is. I can not get the bleeding to stop. There is insulation in the attic but just not where the fan is. I assume when the hot air meets the cool air, condensation forms and I get the wetness.
Any suggestions? Do I need to remove the fan and close the whole then insulate it? There are no ables on the house so a gable fan is not an option. I am considering installing some roof vents to see if that helps.