Is this type of fan appropriate under roof vents in ceiling?

I am going to install a whole house fan to exhaust hot air out of the rooms on the top floor , and while I'm at it I'm thinking of installing fan(s), most likely one (1). in the roof itself to exhaust the air right out from over the ceiling of those rooms. Get it out of the rooms, into that upper area; then why not right out of that area, a hot box.
I have looked into the packaging of one of these fans at HomeDepot. Its just a 15"! (x6"?) circular shroud, and it is to be mounted anywhere- theres no flush mounting or anything, just some metal clips. The pic in the manual shows it mounted so it is blowing Horizontally - out of a louver vent mounted on the front of an "attic" - above the ceiling & below the roof, at the front of the pictured house.
I am thinking I would want to mount a fan under the existing vents on the roof, pointing up and out these vents. I do not want to screw around with the shingles outside. I've got 2 of the std. size approx 12"x12" vents, with screen inside. These vents are only about 7' apart, on adjacent parts of the roof, at the rear. The foof is about 10' x 20'. I am thinking of wiring a switch inside, beside the whole house fan switch (maybe pull cord?), and using metallic shielded cable.
Can I use this type of fan, mount it just below the vent(s) facing up? Will I need to worry about a seal to the vent to create a push vacuum? Do I need to worry about the size(s)/cfm carefully of the fan(s) wrt the whole house fan? Theres soffit venting 360, and 2 vents, need I cover (and seal) both (2) vents with fans?
http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId051&langId=-1&catalogId053&productId0055092 the "interior roof" fan
http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?id0018252&jspStoreDir=hdus&catalogId053&marketID@1&productId0018252&locStoreNum25&langId=-1&linktype=product&storeId051&ddkey=THDSiteMap the whole house fan
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When a whole house fan is used, its drawing cool outside air into the house from open windows and pushing air from the upstairs ceiling into the attic and then out through the attic vents. The air going into the attic from the house is maybe 80 deg? That's not a hot box and in fact the attic should be quite cool and with proper insulation, doing anything else with powered fans isn't going to do you any measurable good.
With the whole house fan, I would be concerned about having enough attic venting to support the volume required. And if you don't I'd solve it with a ridge vent, or maybe another gable vent, not by trying to turn regular roof vents into powered ones.

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the entire 10', 10', 20', 15' x ~6" soffit is by area 1/3 punch vented, then the 2 ~12"x12" vents

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Sounds like you're OK with the soffit venting, but doesn't sound like adquate exit venting to keep the attic cool without the whole house fan, which is what I'd be concerned about. I'd get more venting, most likely a ridge vent which is cheap and easy to install. But if you have a whole house fan going and that is your main concern, with all the soffit venting and the two other vents, there is probably enough venting for it to work. In other words, I'd forget about adding powered fans to the two roof vents. At least I'd put the whole house in first and see how it works without taking on more work and putting in more fans that use power.

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the air, if effeciently exchanged may be less, but I've been reading http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?id0018252&jspStoreDir=hdus&catalogId053&marketID@1&productId0018252&locStoreNum25&langId=-1&linktype=product&storeId051&ddkey=THDSiteMap and the air in there could be 150 it seems, besides I have dark brown shingles
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It can be 150 with poor attic ventilation and no whole house fan. But it isn't going to be 150 with any reasonable amount of attic venting and a whole house fan pushing a huge volume of air in there. With lots of soffit venting that you have, plus 2 peak vents, there is quite a bit of area for the whole house fan to push air out of.
And when do u expect to use the whole house fan? It's of most use when you have cool outside air, like days when it cools off quickly at night. In many climates, there aren't that many days that make it practical. For example, it does nothing about humidity, which further limits it's use. And on days when the attic might be 150, it's going to be 90 outside and most people would have AC on.
Bottom line, in cases where the attic could reach 150, the solution is more attic venting, with or without a whole house fan. And I think the best way to do that is with a ridge vent.
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I bought three 20" temperature controlled box fans ($20 each). Mounted one over the louver vent on the front side of the garage. Mounted the other two on the louver vents on one side of the house. The blow hot air out, and hopefully sucks cold air into the attic from the other sides of the house. So far it seems to work quite well. Way more energy efficient that using the AC all the time. See my more detailed write-up: http://www.gearhack.com/Forums/DisplayComments.php?file=Home/Cooling_the_Attic.html
Chieh
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write-up:http://www.gearhack.com/Forums/DisplayComments.php?file=Home/Cooling_ ... Oh, one more thing. I forgot to mention that if you are going to put in a whole house fan, then you probably don't need powered fans in the attic. The whole house fan will create positive pressure in the attic, forcing air out the vents. It would create negative pressure in the living space to draw air in. You just want to make sure to keep all of these passages open when you turn your whole house fan on.
Chieh
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wrote:

g_...
I read your forum about the fans that you installed in your attic. Those fans appear to be portable household fans. You didn't give any specifics as to how you installed them, however I suspect that they are not approved for the purpose that you are using them for. You should have used gable fans that were designed and are approved for removing air through the attic vents. I hope that you didn't use extension cords to wire these units.
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Thanks. I read your post and responded to it.
Chieh
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Usually whole house fans are used after 6 pm or after whatever time the outside has cooled off enough that it won't warm the inside of the house to suck in the outside air. I guess that could be as late as 9 but I'm not sure.
Usually roof fans go on between 9 and 12 in the morning and off between 5 and 8, depending on how sunny and hot it was during the day.
I'm a big fan of roof fans, but normally whole house fans have enough power to get their air into the attic and beyond, unless I guess there is quite a restriction getting out of the attic. Soffitt vents which are intake vents when using natural convection and roof fans would easily function as exit vents when there is a whole house fan, but I don't know nearly enough to know if your soffits are big enough for this.
I like roof fans if the attic is conducting it's heat to the second floor, but regardless, how about buying one fan or the other and seeing if it is enough. Unless you want one contractor to do it all at the same time.
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On 6/26/07 2:06 PM, in article 1182881238 snipped-for-privacy@sp6iad.superfeed.net, "bent"

A couple of web sites for your whole house fan consideration to check before you decide:
1) http://lib.store.yahoo.net/lib/rewilliams/consumeralert.html 2) http://www.rewci.com/wholehousefans.html 3) http://www.eere.energy.gov/buildings/info/documents/pdfs/26291.pdf 4) http://www.quietcoolfan.com/faq.html ( nice system, expensive though ) 5)http://www.hvacquick.com/wholehousefans.php?utm_source=google&utm_medium=c pc&utm_term=whfans&utm_campaign=whf Great looking system.
Don't forget the benefits of Attic Insulation combined. Especially using a thermal barrier just under your roof decking.
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