We put in a whole house fan a few months ago and it is the smartest thing I ever did. The reason is physics: San Diego is blessed on most hot days with a late-afternoon/early evening offshore breeze. Yet your house heats up from radiant heat and by about 6:00 is actually warmer than the newly cool outside. Solution, open the windows and let that cooler air whoosh through your house and exit into the attic and then out of the attic through standard attic vents. Your house and attic will both be cooler.
This works on all but the hottest of San Diego days. We haven’t had the AC on all summer until a couple of days ago. If this is a normal summer then we expect to use AC only 10 – 15 days, and get by with the whole house fan the rest of the days.
The fan costs $200 – $300 and can be installed by a competent carpenter. Ours is acceptably quiet, but check the reviews first, as some are indeed noisy. A 24″ one is plenty adequate…perhaps the noisy ones cited above were the 30″ fans.
