For example: 2 story house, 20' x 30' with 8' ceilings. A 16 in. 3 spd
fan from Graingers (~3000 cfm on hi speed) is mounted in the trap door to
the attic with a venting window in the attic open.

This has proved effective. Having the fan in the attic is responsible for
the quick cooling to some degree; hot air tends to rise and a fan
pushing out a window moves it less directly.

Hul

In alt.building.construction Lacustral
wrote:
I'd like to use an exhaust fan (fan from a ceiling grille to outside) to
run overnight in the summer, with the windows open, so that my house is cool
in the morning. I'm not sure how much CFM is needed. I don't want a big
powerful whole house fan because I'd like it to be quiet. Just a small
fan that keeps running overnight.

If you're using a fan for that purpose, can you tell me how much CFM gets
your house down to the temperature of the outside air, and how many cubic
feet of airspace you're ventilating, and how long does it take to cool
the house down to the outside temperature?

Just trying to get a ballpark idea.

(I could calculate the cubic feet of airspace in my house, divide by CFM
of a fan, and come up with a guess, but I'm sure it's not that simple -
the hot stuff in the house is heating up the air, fans aren't completely
efficient about clearing out the inside air, etc.)

Thanks
Laura