There are pro's and con's for this topic. Whole house fans are an entirely different device. You need to read as much as possible and decide what you want to do. I have done testing on my house, and do not have a conclusive answer.

Attic fans and attic ventilation are kind of a can of worms, theres lots of different ideas on what works, what is right and what is a bad idea. I had always thought power attic fans do a great job at getting the really hot air out of an attic and reducing the cooling load of an A/C system. I have one in my attic, it probably only runs about 100 hours a year but it does a good job at expelling all that 130 degree air. Other folks like ridge and soffit vents, although they tend to get blocked by insulation.

blacknumber1, do you install attic fans for customers? What brand do you carry?

Sorry, I dont install much of anything, and whenI do someone else buys it and they pay me in beer. Just go to your local HD and see what they have available, theyre not hard to install yourself.

v1rtu0s1ty, your attic should be pretty much sealed from your living space so an attic fan should not effect you air conditioning at all. If you remove air from your attic you should provide a means to replace with outside air introduced into the attic. Some who are giving you advice are probably confusing an attic fan with a whole house fan. Thats a totally different set up and should not be used with A/C

Yeah, looks like you are correct Mr. havac. What I really would like to have is a device that will eject the hot air in the attic then to outside. And for your question regarding replacing the air that we just ejected with outside air, I'm sure that I have soffit vents.

Also, I remember seeing a flexible duct about 6" in diameter hanging in the soffit(top roof) in the four corners of the house.

In my friend's house, just 5 houses away from me, they had an attic fan installed last year. He told me that the installer poke 2 square holes in the roof(shingles). The attic fan gets triggered when attic temperature reaches 85F.

Since I have R38 blown-in insulation, will I really benefit from an attic fan?

my attic used to stay over 145 during the summer. when the squirrel cage motor went out,i was out of town or would hav edone this myself, the HVAC tech said it was the hottest attic he had been in, and he had been doing this for 20 years. i put in a gable vent fan and now it is a tolerable 110 or so up there. the only other thing i have noticed is that my shingles don't tend to curl on hot days anymore, there was no noticeable effect to the HVAC efficiency.

I think my deciding point would be

Does removing the hot air from attic help our A/C in cooling our second floor?

Like in your case David, did you notice any change in the temperature in 2nd floor? Was it easier to cool than it was before when attic temp was at 145F?

Can you guys tell me a recommened/reliable brand/model of an attic fan? I found someone who will does attic fan installation for $225.

Thanks!

Will it help in cooling your top floor? It could, although if the attic is properly insulated, it really shouldn't make all that much difference. What determines whether or not your attic needs a fan is the temperature and air flow in the attic itself. If the attic is getting too hot, it will eventually damage the roof. And if you have electric wiring running in the attic (and nearly everyone does), the combination of a very hot attic and a heavily loaded circuit could cause a fire.

An attic fan may pull air out of the cooled space if there isn't enough air opening to let the fan draw outside air into the attic. When we moved into a house that we lived in previously, it had a fan for the attic (no other outlets other than a single gable vent). I noticed the first summer that when the fan was on, I could feel air being drawn out of the house through and around some can lights in the living room. I went around the house, counted the soffit vents, and did a rough calculation. I figured it needed about six more, so I added three in front and three in back. I also moved away insulation that was blocking several of the existing ones. That helped a lot, and it made the attic a bit cooler too. (Even though during the summer, with the thermostat set at 100F, the fan ran around the clock except for a few hours in the early AM.)

Our current house has a hip roof, but the entire length of the ridge is equipped with ridge vent. And the soffit has continuous venting all the way around the house. I've been up in the attic in hot weather, and although I haven't measured, it didn't seem excessively hot.

i don't have a 2nd floor. it definitely helped cool off the attic, and since the air handlers are in teh attic it took a load off them. you could not leave your hand laying on the handlers before i put in the fan. it honestly was that hot! afterwards, they are cool as a cucumber.

my multiswitch for my directv is in the attic. when i first wired it up it was spring and not hot up there. we added a RX for our daughters room during the summer and i now have a permanent fingerprint scroched on the switch! this past summer, after the fan went in, i ran coax for the living room and the switch was fine.

if you have ridge vents, you don't use a fan, but if not i highly recommend one.

i still need to add some soffit vents myself, my house has none, i just have 5 gable vents.

v1rtu0s1ty - What did you end up doing on this? I am in a similar situation as you and am at a loss. I have spray foam insulation on the underside of my roofdeck which sealed off my ridge vent (and most likely my soffit vents if I have any that is) and it is still over 80 degrees in my second floor even with my second floor heat pump unit running 24/7. I have been considering adding attic fans to my gable vents and either opening up or adding soffit vents to replace the air, because at this point I don't know what else to do. All I know is I am paying huge electric bills to still be hot.

Guess it all depends on your application. In my particular situation the power vent reduces the cooling load on my central air and keeps the house cooler with it running. Although I suppose if the attic was better insulated there would be minimal difference. Another factor to consider is operating cost and maintainence. Power Roof mounted vents require lubrication. Few are made with sealed bearings, so that means an annual or semi-annual trip to the attic to oil the motor. The hotter it is up there, the more the oil wicks dry up in the intense heat. Plan on replacing the motor also, they are notorious for failure. I have replaced one in a very short 2 year period. And finally the electric cost to operate them sometimes 10+ hours a day negate any savings to the HVAC running less. Other forms of attic ventilation can utilized at a much cheaper cost. Aside from being a fire hazard, if your leaving on vacation for a period of time, I would also kill the power to it also.