I'm considering putting in a couple of powered attic vents. Despite a lot of anecdotal evidence, I'm not sure how much difference they'll make to the temperature inside the house. We live in a high desert environment (Carson City, NV); the single-floor house is 11 years old, and is quite well insulated. It has 2x6 exterior walls which are full of fiberglass, and there is about a foot of blown insulation in the attic. What's giving me pause is some measurements I've made with a handheld infrared thermometer. Readings taken at 3 PM and 8 PM show only one-to-two degree difference between interior walls, exterior walls, and the ceiling. Will one or more attic fans make a significant difference in the indoor temperature?
Here in Middle Tenn, it's a very good idea, I'm installing 2 or 4 next week and probably 10 next month, I've proven to myself, they can relieve up to 12,000 Btu-H of heat gain for some houses
and unmeasurable damage to the roof and especially if you store items in the attic. After last years 105 degree Summer, it's a cheap savings all the way around.
Since I own an HVAC company, I'm using a fan and bracket from a 5 ton condensing unit to cool my attic, because it's 220 volt, it draws less power, but it's stronger.
If you have gables with real louvers, not the plastic/vinyl preforated triangle, get a measurement and get the biggest fan you can use, then cover up any roof vents that are
close by so you can get a cross breeze from the far end, if no gable(s), then roof mount is the next best thing.
You need to look at the temperature difference between your attic and the outside. An attic fan is only going to equalize these two temperatures. If you only have a 10 degree difference, I suspect it won't do you much good. Probaby, if your house is fairly new, it has adequate passive ventilation.