A key point that seems to need underlining here is that there
are two elements. The air exhaust (via fan), and air *intake*.
You can put in a humongous monster of a fan but if you don't
open enough windows and interior doors throughout the house,
the fan cannot get enough house air to exchange hence cannot
cool the house. This is especially true in a newer, "buttoned
up" heating/AC efficient house.

Also, a good reason to install a whole house fan in an attic
gable end (if you have one) is so that you have the choice of
running the fan to cool just the attic (indirectly cooling
the house, but with less perceptible noise and no draft), or
to cool the whole house directly, by opening the attic door,
selected windows, and interior doors (especially the bedroom
doors).

Catalogs (and websites) that specialize in farming equipment
usually include a huge selection of ventilation fans.

Una