New Garage Gable Fan - Are They Efficient?

[Don Ro]

Building a 20' wide garage extension onto my existing double garage (already attached to house) and thinking of a thermostatically controlled gable fan.
My intention is to lower attic temps during Arizona hot days.
Reading up on the issue I see some say it's a waste of time, energy, and $$.
What say you gurus?
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Any product info about high quality, durable fans?
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TIA

[Tobra]

Maybe make it solar powered. My understanding is that the ridge vents work a bit more efficiently

[Don Ro]

What's a ridge vent?
I now have two turbines on house roof.
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House has gable vents on both ends...one is on the attached garage.

[ckelly78z]

A ridge vent is where the peak of the roof has an airslot that allows hot rising air to escape. Rather than nailing shingles over the peak, a long metal vent is installed to allow airflow.

[VincentVega]

Normally fans in the attic suck air from the house, cooling the attic some but also raising your cooling bills. Not usually an issue with a garage. If the attic connects to the house, try and air seal any gaps, usually electrical boxes and lights are the biggest voids but some houses have them everywhere.

[vash]

my next door neighbor installed one. she is an elderly lady and her repair guy cracked me up. he put up a fan that is more at home on the side of a 7-11 convenience store than on the side of a residential home. it came complete with nice rattlly, sheet metal louvres that fly around in the breeze. the sound that thing makes cracks me up. the man living directly across the street from her damn near freaked out when it first got installed. it is very loud in his front yard. turned off, the louvres fold down and i guess keep bugs out..she turns it on, and the louvres get lifted by the wind.. i laugh every time i see it dancing about.

having said that..her garage is cooler than mine.

[ckelly78z]

On cool nights in the Summer, I leave my garage doors open, because the entire ceiling of the garage, is the floor of the bedroom above it.....(big bedroom).

[flipper35]

Originally Posted by ckelly78z

A ridge vent is where the peak of the roof has an airslot that allows hot rising air to escape. Rather than nailing shingles over the peak, a long metal vent is installed to allow airflow.

Around here the shingles are nailed over the vent to make it look much nicer. They still work the same and let it vent very well.

[speedster911]

Not sure of AZ temps but in NO CA i have fan set up to thermostat- surprising how much air it moves. garage is over insulated and I think I get more benefit from great insulation vs. fan related to keeping it cool. When temps drop in the evening- sucks all the accumulated hot air out very quickly.

I have mine on a switch so I can turn off if I chose. the thermostat is adjustable. I think I have mine set @ 105 before it kicks on but can go as low as 75.

[cashflyer]

End fans for cross-draft cooling.

[Eric 951]

Don,

Will your garage be open to the roofline , or will there be a ceiling with space above up to the roof?

Unless paired with a supply fan (or intake louvers) on the opposite wall for a cross draft (as cashflyer posted), a stand-alone exhaust fan located in the gable is not worth it. You ideally want to create airflow and there are (2) efficient ways of doing so.
Intake air near the ground level and exhaust it through the roof(ex. windows or garage doors being open to draw air in) and roof-mounted turbine vents (the mushroom-looking vents), a true ridge vent, or powered exhaust fans mounted on the roof--all are designed to vent the hot air out just as a chimney operates(gravity ventilation).
Yes, this will also work on a limited basis with a wall-mounted exhaust fan to vent the hot air but is not nearly as efficient as a roof-mounted exhauster, and you have no means of moving the air to the single wall fan location--a lot of hot air will remain trapped.
If you are mounting in a wall for your exhaust, your intake should be on the opposite wall to create a cross-draft.
For your application and the added expense of installing a single powered wall exhaust fan, you would be better off going with a fixed gable vent instead of the powered fan, or one of the roof options mentioned, or a gable vent and a ridge vent.

[Don Ro]

Thanks for all your replies...I appreciate the participation.
I will restate what I've already written:
- ...thinking of a thermostatically controlled gable fan.
- - House has gable vents on both ends...one is on the attached garage.
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As is, my house has two gable vents, one at one end of the house and the other at the opposite end - which is the existing garage gable vent.
At the side of the existing garage where the garage gable now exists, I will be using that wall and adding another 20' wide attached garage - three more walls for the new attached garage.
An existing outside garage window will be removed and a set of doors will be installed to allow access from the existing garage to the newly attached garage.
So, in the end, there will be an attic air corridor from the end of the newly attached garage all the way through the house attic and to the other end of the house...the house's existing gable vent.

Eventually, there will be a garage gable vent > at the garage attic > through the house attic > to the house gable vent on the other side of the house.
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What I thought about doing is installing a gable fan at the new garage gable vent.
Blowing the hot attic air through the garage attic and out the other end, which is the existing house gable vent.
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So if a breeze is optimal, and a female cat in heat hangs out at the new garage's gable vent, a horny Tom cat hanging out at the house's gable vent on the other end of the house will become aroused.
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Sorry if I was not clear.

[flipper35]

Wouldn't it be more efficient to suck the air through?

[Don Ro]

^^^
You tell me. That's why I'm asking the PPOT.

[Don Ro]

If sucking the hot attic air though would be more efficient then I'll install a gable fan at the end of the house.

[tcar]

If you have an exhaust fan (or turbines) at the top of the space, where does the make-up air come from? Open window? Louver in the door? Should be low in the space.

Turbines will do a pretty good job if there's adequate air supply.

Should not suck air from the house... that's against fire code anyway.

So, if it's 130 in the attic and 120 outside there in Dismal, kind of a waste of money.

[Don Ro]

Two turbines presently on the back yard side of existing house roof.
Are you saying I ought to just add a turbine to the new garage roof?
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On a 100 - 120 degree day here in AZ, wouldn't the attic air be around 150+?
I'm surmising.

[Don Ro]

I just read that in AZ the attic air can reach 160+.

[RKDinOKC]

When i redid the shingles and had to scrape the layers down, took the turbines off, put in a ridge line vent, and added more vents to the eaves. It is a lot cooler.
You leave about a 4 inch gap at the top of the ridge. Then put a little roof over that with a gap under it. The little roof covers enough that wind blown rain is kept out and not enough gap that the animals get in either. But is more venting that the two turbans did, and the convection works really well.

The main ridge line of my house is North to South. Garage and a bedroom stick out to the West on each end with their own Gables a little lower than the main ridge line. Makes like a U. The bedroom was on the North West end. Before I did the ridge line vent and an extra eave vents the temps in that bedroom were 5 degrees warmer than the rest of the house. Brother with MS was staying in that room and ended up putting a window A/C to keep it from getting too warm for him and freeze the rest of the house. If it got above 72°F he would start sweating and become paralyzed from the MS. After putting the ridge vent and extra eave vent in that room stays the same temp as the rest of the house and was able to get rid of the window A/C.

The only problem I had with the extra eave vent was too close to the stockade fence and the squirrels got in before I figured out the wire on the new eave vent had to be squirrel proof!

The garage walls are not insulated, the door is with weather stripping. The temp in the garage is cooler than outside in the summer and warmer in the winter...until you open the overhead door. Then the ridge line vent sucks outside air through the heater closet and gets it to match outside if the door is left open too long. Did go from two 1000watt heaters in the garage to just one to keep it above 50°F on the coldest winter nights after going to the ridge line vent.

[Don Ro]

I've decided to follow the suggestions of the builder.
The new garage will be finished with insulation (walls 'n attic), sheet rock, etc.
I have a couple of portable air conditioners if I want to work in there during the heat of the summer.
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Thanks all for your replies.
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