Attic fan useful?


Old 04-16-07, 01:11 PM
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On a related note, the area I live in seldom gets above 90 degrees and low humidity. My ceiling is insulated - would an attic fan (the kind that blows air from the attic to the outside) be useful for me?
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Old 04-16-07, 01:28 PM
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In my opinion, no. However, in my opinion, such things aren't really that useful even in Phoenix. Make sure your attic is well ventilated with eave vents and vents up high (either ridge vents or those circular capped holes), and gable vents if you have gables. And install wind turbines if you want. But in an attic that is well ventilated and insulated, I don't see how the benefit of an attic fan will outweigh the cost of the electricity to run it.

I know that other people have other opinions on this. I've never seen a scientific study of the subject.
Old 04-16-07, 02:20 PM
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I'll have to both agree and disagree with John's comments. (since it's not a directly electrical question, I feel I have the possibility of not being wrong

As John stated, if the attic is properly vented, with a considerable amount of eave vents and ridge vents, the natural convection of heat rising, should be enough to cool the attic to keep it almost the same temperature as outside.

The problem is, every house I've ever been in, has not been vented properly or enough. Most people (and builders?) think that a 12"x18" gable vent and maybe a ridge vent is enough to properly vent an attic. Well, when you go up there and it's 110 degrees on an 80 degree day, I beg to differ. In that case, I've found an exhaust fan can work wonders.

One example, in a house I was "flipping", just installing a roof fan lowered the attic temperature a good 15-20 degrees on hot days - and even helped cool the upstairs rooms.

So long answer short - I think the answer is a combination of good venting and an exhaust fan.

Question back to you - when it's 90 degrees outside, how hot is it in your attic?
Old 04-16-07, 04:15 PM
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Originally Posted by Zorfdt View Post
Question back to you - when it's 90 degrees outside, how hot is it in your attic?
I just bought the house this winter, so I'll have to get back to you on that! ;-)
Old 04-17-07, 05:42 PM
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It is interesting to note that the same night I read this thread on a local TV station ( there was a story on a house being built here in Houston with a sealed attic with no ventilation. Instead the attic will be cooled by the central AC just like the rest of the house. The story said that doing that may cut electricity use by as much as one third. Not much more detail given but it is certainly an interesting idea.
Old 04-17-07, 05:50 PM
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I tend to agree with John, I use a combination of wind turbine and good venting. The wind turbine can be put to in use in more than one area if the duct work is run properly. I use the turbine to help cool both my attic and the top level of my house and it works wonders on hot nights.
Having said all of this, the fan may be the right answer in other climates as I live in area with a very moderate climate (highest temp is usually 30 deg Celcius approx 90deg F) and we dont see too many of those days.
Old 04-17-07, 06:16 PM
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Ill go this way. A roof turbine is no good at all . When you do need it there is no wind so it just sits there and dont do a thing. Then a storm and wind comes and the rain comes in it . Most in Fl now are out lawed. Because of that. If you have the attic vents you need for you attic 1/2 in and 1/2 out no you dont need a fan for the attic . But if tight on vents a fan sure will help Also if you have a tile roof the fan helps a lot. also with the ridge vents they have had them where the wind blowes the rain water back up and in it . As the water cant get over the ridge with it there

ray2047 I sure dont want to be the one that pays the electric bill for that. A lot of attics can hit 140o if not enough vents in it
Old 04-17-07, 06:32 PM
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We didn't catch where you are. Here in San Diego, minimal rain so turbine ventilators are quite helpful..certainly worth the cost. They operate on natural updraft from the temp diff, so do not require any wind.

If your house is air conditioned, then any amount you can cool off the attic will probably make your house more comfortable. If it is not air condiditioned, it will help to reduce heat gain during the day and help it be cooler at night.

Ehaust fans do not need to be very big, so the electric cost would not be huge. The payback is partly in dollars and partly in comfort.
Old 04-17-07, 07:54 PM
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I am a big fan of whole-house fans. Of course, they don't help during the day, and you can't run them at the same time as your air conditioner. But if you're gone a lot during the day, and you live in a climate where it cools off in the evening (i.e., not Phoenix), they're great. They cool off your house and the attic at the same time. It's good to improve your attic ventilation before putting them in so that the air you blow up there can get out.
Old 04-17-07, 08:09 PM
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You might get more opinions if this thread is moved to the "Ducting, Air systems, and Ventilation" forum on this website.

Seeing that you are in California, I do not feel that a roof mounted attic fan would be necessary for your situation. I would go with good ridge venting with plenty of soffet vents.

I second the whole-house fan idea. I have a belt-driven blower mounted in the gable end of the attic, which draws air through both the house and attic. I only have two outside vents in the attic, so the fan draws outside air into the attic, as well from an attic mounted automatic shutter in the upstairs hallway ceiling. It works great!

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