how to keep garage attic cool

[87GN]

I had a 1200 sq ft garage built last year. I'm trying to get the attic temps down. Right now, they are about 30* above the temp in the garage. I had fan installed that turns on at 85*, but it still goes to over 108* on a 80* day and summer isn't here yet. The attic is about six feet high in the center. I have acces to the attic using pull down stairs which I pull down to get some air flow up there. Would another fan blowing out (or in) intalled in the vent on the end of the side of the garage help? Thanks.

Mark

 

[bobbyd]

I had fan installed that turns on at 85*, but it still goes to over 108* on a 80* day and summer isn't here yet.

Is there a way for fresh air to get in? Without the appropriate intake vents in the soffits, the fan will be ineffective. What is the cfm on the fan?

The volume of your attic should be about 3675 cubic feet (this is just an educated guess since I don't know the dimensions of your garage). Even a small 500cfm fan can completely replace all the hot air with outside air in about 7 minutes, if there is 500cfm of fresh air available through the intake vents.

 

[camarojoe]

What kind of a fan do you have that will automatically turn on at a specified temp? Do you have it wired into a thermostat? I have a standard box fan up in my attic that I turn onwhen its hot, but I don't like letting it run indefinitely, especially if I'm not home.. Its just plugged into a standard outlet I installed in the attic with a switch downstairs that i can use to turn it off and on without crawling up in the attic..Would be cool if they made some sort of "plug-in" thermostat that would kick on the power to the fan at a specified temp... I don't think something like that exists... or does it?

 

[87GN]

Thanks for the replies. There are vents in the soffits and a vent on each end of the attic. The fan is rated for 1650 sq ft. Looking at your calculations, the fan is not large enough- or is it?. the gargae is 30' x 40'. The attic is 6' tall at the center of the rafters. I'll have to look at the photos I took of the box to see if I can read the cfm rating. It is the fan the builder installed. The garage was finished last fall and this is the first summer I'm having with it. Can I have another fan installed on one end to draw air into ( or out of) the attic?

Camarojoe- the fan is wired to a thermostat that I set to turn on at 85*. It has an adjustment knob to set the desired turn on temp.

Thanks again

Mark

 

[bobbyd]

Your attic is about 3600 cubic feet in volume. Attic fans of this type are sometimes rated in square feet, particularly when marketed to homeowners that don't know much about construction. In this case, yours appears to be big enough, but the true measure is its CFM rating. This will tell you how quickly it can replace the entire volume of air. The problem is that the manufacturer says it will handle 1650 square feet, but does that mean 1 air change per hour or 10? The difference is huge.

A fan of this size will require on the order of 5 square feet of intake area. That's something like 18 4"x12" soffit vents considering a free area of 80% or 13 6"x12" vents.

Also, and I'm sure you have, make sure that the polarity on the fan motor is correct and is blowing out. Won't be very efficient if reversed and there is only one.

 

[bobbyd]

CamaroJoe,

Here is a link to a thermostat that will meet your needs. Just wire your box fan through it to the outlet.

http://www.grainger.com/Grainger/wwg/productIndex.shtml

 

[gary whipple]

You might consider these vents:
http://www.roofvents.com/

I have 6 of them sitting in my garage ready to be installed.

Gary

 

[dboat]

Or this...

http://www.cor-a-vent.com/

 

[rogabbott]

Here in the hot southwest, before universal air conditioning, many older homes were built with an "attic fan" - a fan with 36" to 48" diameter installed in the ceiling, most with louvers that close when it is off. These fans may be direct drive but most are belt driven with a 1/4 hp motor. They are capable of moving lots of air through the house, into the attic and out through the soffit vents. This may be a solution - ventilate your attic and provide some air flow through the garage as well when you are working. Of course, it won't work if your garage is completely shut up: there has to be a source for incoming air. I think Home Depot has an attic fan but I would prefer one taken out of an old house to match the antique junk decor of everything else in my garage.

 

[bhays]

Here in the hot southwest, before universal air conditioning, many older homes were built with an "attic fan" - a fan with 36" to 48" diameter installed in the ceiling, most with louvers that close when it is off.

I just finished putting one of these in. I got it at my local Ace Hardware, it's 36" 6900 cfm...

http://www.garagejournal.com/forum/showthread.php?t=4619&highlight=attic+fan

 

[camarojoe]

CamaroJoe,

Here is a link to a thermostat that will meet your needs. Just wire your box fan through it to the outlet.

http://www.grainger.com/Grainger/wwg/productIndex.shtml

Link won't work... can you repost it?

 

[87GN]

Wow!!! Thanks for all the replies. The fan is rated at 1170 cfm. Is this enough?

Mark

 

[dboat]

Remember that his fan is not insulated.. there are insulated versions though.. but they are not cheap.
Dana

 

[Jay H 237]

We have a whole house fan identical to the one in the post on the last page. During the winter, since it isn't insulated, we cover it up with an old comforter from a bed. This has stopped any drafts we had.

The comforter is wrapped around it up in the attic and when spring comes we unwrap it until the fall.

 

[dreamingmuscle]

Try this link

http://www.grainger.com/Grainger/wwg/itemDetailsRender.shtml?ItemId=1611774194

Or ou could buy one of these just plug it in and set it to come on during the hot time of day.

http://www.grainger.com/Grainger/wwg/itemDetailsRender.shtml?ItemId=1611756865


Glen
________
Dodge Copperhead history

 

[87GN]

Thanks again for all the suggestions. The garage was finished late last year, so this is my first summer with it. I'm not looking to cool the garage itself, just the attic where I store my stuff. There already is a thermostatically controlled roof mounted fan set to turn on at 85*. But, it still gets to about 104* during the day. I'm looking to pull more air through the soffit vents, trying to lower the temps. If I were to install agable fan, I "assume" I'd install it to blow the hot air towards the outside as opposed to pulling outside air into the attic and have the roof fan exhaust it out? Is there a way to verify the soffit vents are clear. The builder blew this fluffy, loose insulation on top of the ceiling in the attic. Could this clog the air inlets?
The garage is 30 x 40. The useable attic space (plywood nailed to the center of the roof trusses) is 30 x 12 x 7 at the center and the loose insulation on either side towards the soffits.
The picture is a view from the front to rear of the garage, showing the attic floor. The rectanglular box in the floor is the pull down stairs opening. The attic fan is not yet installed, but is located towards the center of the roof. The is a vent on each gable end.

Thanks.
Mark

 

[hemi]

GN87,

You may want to investigate a radiant barrier paint made by Sherwin Williams co. This paint is specifically made to be applied to the underneath side of osb/plywood roof sheathing. It reflects the radiant heat before it gets to the attic. The paint is sold under the name E-Barrier paint and its silver in color (too bad its not chrome since it does'nt go fast). Its not cheap at $40/gal. but covers 350 sq ft per gallon. Thats my story and I'm stickin to it..
hemi

 

[dboat]

GN87,

You may want to investigate a radiant barrier paint made by Sherwin Williams co. This paint is specifically made to be applied to the underneath side of osb/plywood roof sheathing. It reflects the radiant heat before it gets to the attic. The paint is sold under the name E-Barrier paint and its silver in color (too bad its not chrome since it does'nt go fast). Its not cheap at $40/gal. but covers 350 sq ft per gallon. Thats my story and I'm stickin to it..
hemi

I've seen this stuff demo'd and it was impressive.. they should make ever house in the south have this painted on the inside of their roof..
Dana