Is it appropriate to mount this type of fan under existing roof vents?

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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whoops, sorry, this goes in a.b.c & a.h.r
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NO. Soffit vents are necesssary. The one fan you choose is a gable mounted fan. These are used in conjunction with your soffit vents. Basic venting depends upon convection to draw cooler air through the soffit venting. A Ridge Vent is typically the most efficient approach as it vents through the highest point(s) in the structure.
The House fan is designed to pull cool air through the windows, scree door(s) etc. venting it into the attic where it should exit via existing roof vents. However, if the square footage of the existing vents is insufficient, the effectiveness of the House Fan will be similarly diminished.
There may be a formula somewhere that will give you the minimum sf of venting required in soffitts and in roof for basic convection venting. I would suspect that forcing air into the space might well reuire an incrase in the roof venting to handle the increase flows of air.
I have four 6" passive vents mounted (previous owner) and find he house fan forces air out through the Soffitt vents - because, I assume, I need larger (or more) roof venting. I willl install a ridge vent when we re-roof and have two powered roof vents (thermostatically controlled) to install in each gable end as well.
Good Luck

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I am building a 12' x 20' workshop, and as soon as I put the roof on (gable), I could tell that it is going to get very hot in there when it is closed up. I don't want any windows, to increase wall space for storage, but have double doors that I will keep open when I work, as well as my dust system. I have installed an automatic venting gable fan on one end of the building, and my question is, should I put a vent in the opposite side of the ceiling, or somewhere on the base of the walls?
Thanks, Tim
Hoosierpopi wrote:

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