Roof Mounted PW Vents Worth The Electricity?

I have a pw vent mounted to my house that doesn't/didn't work. (came with the house in 84) Just recently I bought a new one and got REALLY lucky, I only had to replace the motor the housings were the same. Three blots!
They say to set the thermostat at 105 degrees, I have mine set at 110 and the fan kicks on at about 12:30 pm everyday and shuts off at about 6 pm everyday.
As we know it's not even summer yet and this thing is already running 5-6 hrs a day.(most days, some days it doesn't even turn on) BUT, I live in Fl and have a feeling that the closer we get to summer, the more this thing is going to run.
I've looked at the electric meter outside and it's not really using a lot of pw. Looks to be about the same as a ceiling fan (about 85 watts?)
I have a thermometer in the attic to monitor this thing and it does keep my attic at 105 degrees, (on one side of the house anyway, they recommend using 2 of them with a 2000 sq attic - 6/12 pitch roof.
Well needless to say I'm not going to put in another one. (i don't think, LOL!)
My attic is well insulated so whether it is 150 degrees up there or 105 degrees up there, is it really going to make the INSIDE of my house any cooler?
I mean the way I look at it, if you have enough insulation in your attic the heat isn't going to penetrate all the way down to your ceiling anyway, so whats the point of using these pw vents?
Is it just a waste of pw?
BTW, I have 3 regular 24" long 6" tall vents in my roof also. No ridge vent or gable vents.
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"My attic is well insulated so whether it is 150 degrees up there or 105 degrees up there, is it really going to make the INSIDE of my house any
cooler? I mean the way I look at it, if you have enough insulation in your attic the heat isn't going to penetrate all the way down to your ceiling anyway, so whats the point of using these pw vents? "
If it were perfectly insulated, that would be true, but normal insulation is far from perfect. That's why the temp on the other side of the insulation makes a difference and one of the reasons why heating/cooling systems run more the bigger the temp difference. Proper attic ventilation will help reduce the temp diff and result in less cooling demand on your system. I think one of the bigger differenced is with proper venting, once the sun goes down, the heat gets removed from the attic quickly instead of staying trapped there for many hours.
As Joseph pointed out there are other reasons for proper venting, ie moisture, roof life, etc. IMO, for most applications, the most effective system is adequate soffit vents and a ridge vent. With a fan, you have to be especially careful that there are adequate intake vents for the fan capacity. Otherwise it can suck cool air out of the living space through recessed lights, cracks, outlets, etc.
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It could increase cooling costs by removing cooled air from below up through your attic. It depends on how well your house is made. Usualy alot of static venting is all you need. Every house and location are different so it isnt that simple. Be sure you have the proper static venting first then see if the power vent helps in your situation
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Ron,
Advanced Energy, a building science organization group in NC has a page on attic exhaust fans. Go to
http://www.advancedenergy.org/buildings/knowledge_library/ventilation/attic_ventilation.html
You should find it interesting.
Stretch
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Ron wrote:

It will make some difference to your comfort in your home, but more important it will also make a difference in the life of your roof and structure.

You need two sets of vents. One set low like soffit vents and one high like ridge or high gable vents. Hear rises and if it can go out the top and be replaced with cooler (less hot) air coming in the soffits, you should not need any power venting.
Depending on where you live good venting also prevents ice dams and related damage, a power vent will not help there as it will not be on.
I suggest you have someone local evaluate your current venting system and make sure it is designed properly and functional (like soffits not blocked by insulation.)
--
Joseph Meehan

Dia\'s Muire duit
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Trader & Joe, The house has plenty of soffits running the entire length of the house front and back. And, they are open, I've checked them. As a matter of fact when the fan turns on there are a couple of places outside of the house where I can hear the air being sucked thru the soffits.
Like I said, the pw vent came with the house in 84 (a couple of other houses in the neighborhood have the same set-up) so "hopefully" the builders knew what they were doing.
BTW, were underpaid Mexicans building houses in he mid 80's? : )
Just a JOKE ppl don't get offended.
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Well ... I've been in attics with powered vents, and attics with ridge vents .... the attics with correctly installed power vents are always MUCH cooler than those without.

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On Sun, 10 Apr 2005 10:50:21 -0400, snipped-for-privacy@webtv.net (Ron) wrote:

I'm also in FL and sounds like we have similarly vented attics. I keep the set to 120 on the attic ventilation fan. When it is 95 outside with the sun shining the fan is never going to be able to cool to 105 so it is going to run all day long. Set at 120 mine comes on around noon and cuts off around 6 or 7 in the summer. Other than that I don't hear it come on at all and pretty sure it hasn't come on yet this year.
Steve B.
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