I've never liked the attic fans. If the cieling is insulated well and you have good ventilation in the attic, I can't see running something that raises the electric bill- trying to lower the electric bill. If you had a ridge vent installed instead (with the soffet vents) you wouldn't need a fan and you would allow convection to do the job for free.
Attic fans motors sit in hot attics and don't last as long, you don't know if they are working all the time, and also are a fire hazard.

Neil:
Also in NorCal here and after a year of keeping records, I can safely say our attic fan does nothing at all for keeping the place cool, and it's a good one. We put in extra venting and the temp in the attic is considerably lower now. We have a very well insulated space now (post-remodel), with a very good radiant barrier, and have only run the a/c once so far this year, for about an hour on the third day in a row above 100. I've kept track of temperatures in the attic compared to the outside and inside, and on days with similar outside temps I see essentially no difference in the inside temperature whether or not the attic fan is on. Attic temps were 3-5 degrees lower with the fan on, but that doesn't seem to make much difference for the inside temp. I've read that unless you have a very tight house, the attic fan can suck cool, conditioned air out of you living space, as well as out of the attic, meaning the fan actually makes things worse.

I'd advise putting in the extra venting first and then see if you still want to try a fan.

Thank you all for the feedback.

I have an almost-new shingle roof, installed by previous owners who added essentially no venting. I called several roofing companies, and two HCAV companies, all of which unanimously recommended against adding ridge vents to my roof (almost 4' high hip) due to cost reasons. They said the attic fan would be cheaper, cool even better, as well as save a good chunk of air conditioning money.

On a day like today in the Bay Area, my attic is up at about 55C now. Unfortunately I have only about 3" of blown insulation between ceiling and attic (and none in floor or walls) but need to replace tons of knob+tube wiring running all over the place before I can really put in the thick stuff.

Thanks

Neil

All we did was add soffit and gable vents, no ridge vent except above the main living space, which has cathedral ceilings and no attic. Total cost of the gable and soffit vents was less than $50. The difference in the remaining attic space was dramatic.

I'll say it again, whether or not my attic fan is on has made NO difference in the inside temperature in the house. I researched the heck out of this, and found no definitive study or demonstration that shows that attic fans will actually save you money on your energy bills, but found quite a few showing that they have either no effect or a negative effect.

If you can find any reliable study or source saying otherwise, I'd like to see it. I've found plenty of unsubstantiated claims about savings, and like you have heard dozens of professionals in the field saying it will save money, but have seen no real study proving they actually save money on energy bills. And with an old house like your's, which are generally not very tight, attic fans actually make things worse.

Thanks Matt.

Did you find just adding the soffit and gable vents made any difference to the _interior_ temperature of the home? Obviously I can't add gable vents, but when I install the soffits myself maybe I'll look at adding some more vents on the side of the roof to go with them, and see if that makes a big difference before thinking of fans.

Neil

We added powered attic vents about 8 weeks ago (2 GAF units, about $70 or so apiece). They have t-stats on them that turn them on/off automatically at a specific temp setting. I can hear them when they are running, but they are not very loud or objectionable.

So far it seems to have helped a lot with our AC. In the past when it hit the upper 90s the AC had to really struggle to keep up. Now with the new vents it is keeping up with the cooling needs in the afternoons.

Our attic gets (got) hot. Really hot. It's a shallow pitch (maybe 3' or 4' at the center peak). We have soffit vents but those did not help the heat build-up at all. Our house was built in 1960 and is not as tight or insulated as modern places. So in our case the powered vents have helped a lot.

Neil:
I didn't start keeping detailed temp records until after our venting was done, so I can't say for sure, but it seems that it really didn't make that much difference to the inside temp. Warm air rises, so it doesn't come down from the attic into your living space very easily, especially if you have decent ceiling insulation with a thermal barrier.

The attic temp dropped a good 20 degrees after increasing the venting, and now stays about 10 degrees warmer than outside. I was working around the soffits over the weekend and was amazed at the amount of air coming out of the vents on the down-wind side of the house.

One thing that helped a lot was using vent chutes to make sure the ceiling insulation doesn't interfere with the air flow. Check the link below if you don't know about them.

Here is a link that might be useful: Vent chutes

Howdy all,
My attic fan took a leave of duty, and when I called around to replace it, someone talked me into a whole house fan, as it vents the house and the attic. Wow, what a difference. I think the attic fan did nothing but make noise. Now upstairs is actually cool enough to sleep.
Cheers, Jake