installing gable attic fan

I want to install a gable attic fan one above the master bedroom which has it's own attic. The picture inserted is above the master bedroom. It has just one gable opening with eave vents all along both sides of it's roof. From what I've seen gable fans are larger than my opening and I'm not sure what to do. I really do not want to make the opening larger which will entail messing with the siding on the outside. The gable also has rafters directly in front with only a few inches between the rafter and the wall/gable opening. Any advice/input would be appreciated. Thanks in advance.

I also want to put two gable fans above the main house attic later on.(one to draw the air in and one to suck it out). These are triangular in shape and also do not look that large. I haven't measured those yet.

 

Let's start at the beginning. What's the ultimate goal? Is it to cut AC costs in the summer?

 

I think we're going to the same place. IMO your needs will probably be met better and more passively with soffit and ridge venting, rather than the gable fans. We'll wait on your ultimate goal for further comment.

 

Yes it is to help cut the AC cost but also these attics are extremely hot, sweltering in fact. I'd like to get air circulating through them.
My attics have the circular soffit vents all along the soffit. We don't have ridge vents. We re-shingled our roof about about a year ago and if I had thought of it then I would have put them in but I'm not about to tear the roof up now.

 

When you say "circular vents" my first concern is, is there enough vent area, both in and out. Generally you want more effective area on those soffits than you have in the gable and both combined need to meet the 1 sq ft for every 150 sq ft of attic floor calculation. Both gable and those circular soffit vents need to be reduced by their "net free area" to determine their effectiveness.

Bud

 

Why would you have to touch the roof to install soffit vents? Aren't they installed below the shingles in the soffit, itself?

 

You don't have to "tear the roof off" to install ridge vents. A good roofer wouldn't have left it without ridge vents. You just have to take off the ridge cap and cut on either side of the ridge about 2" and replace the ridge cap with ridge vents and ultimately matching shingles for "pretty".
And what Bud said.