habbi wrote:
I am building a new house (2000 sf and probably 30000 cf with vaulted
ceilings) and want to install an exhaust fan in the attached garage. My idea
is that it will get rid of welding smoke, saw dust etc.. but mainly I want
it for cooling the house in the summer. Open the a window at opposite end of
house, open window in the door between garage and turn on fan. I have no
idea what CFM to get but was thinking about an 18" model rated at 3200 cfm.
It uses a 1/3 hp motor. Can these be slowed down if to much air is moving.
Can any motor be slowed with a speed control or are certain motors only
designed for this. I guess I could put a smaller fan blade on to reduce
flow. Thanks

As others have said, this can be a bad idea for fire reasons.

If I was doing it, I'd want to make the inlet from the house through a
couple of meter conduit, with a couple of doors set to fall on 45 degree
closures, at the failure of a fusible link (both doors at once) at 50C or so.

I would be more tempted to seperate out the two fans.