"DA" wrote

It sucks conditioned air from inside the house into the attic? Is it a
finished attic? Otherwise I can't see any logic in using this fan. Sounds
like the only speed setting you'd want on it is OFF.

Whole house fans suck fresh air from outside through the open windows and
door and push it out the attic. On cool nights, it is a very efficient way
of cooling down the house. It does not replace AC on hot and humid days.