I've installed several gable exhaust fans in my house and garage, and in each of them I made a template out of plywood to fit around the fan and block off the area of the gable vents that the fan didn't cover (these are all fixed louver vents). I did this on the advice of a friend of mine who's been in commercial HVAC for 40+ years. He said without blocking the area of vents around the fan there will be blowback, but in addition the fan needs to be pre-loaded. My father keeps telling me I'm going to burn out the fan motor but so far I've had no issues. Who's correct in this scenario?
"grumpy", this is the way I do them also. One extra thing I do is to add an inline fuse in case the fan locks up and the wiring gets too hot. Too many homes around here in the last few years have burnt to the ground and the Fire Marshall's ruling was that the fan had quit and the electricity was still there heating up the wiring. I've done some survey's recently at both of our apron stores and I have NOT found a ceiling exhaust fan with built-in overload protection.
I think the fixed louvered vents with a screen restricts air flow too much. I always install a shutter vent in front of the fan. The fan's on, the louvers open. The fan's off, the louvers close.
This way the fan has minimal restriction.
"They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety."
B. Franklin 1759