Need gable ventilation

[crabo]

I have a large 2 car detached garage. I want to put in a gable mounted fan with louvers to take the heat out of the ceiling. Anyone know what cfm I should look for? The garage is about 650 sq feet.

Thanks,

[tryNto]

I think even the smallest one will be way more then you need.
@650 sqf I would get the smallest/lowest cost I could find.

[runfiverun]

650 cfm is a medium sized 4 bbl carbeurator.
c'mon craig :lol: just put a holley up there and open it wide.

one of those rotor twirly gigs should vent for you easily enough.

[Charley]

How high is your ceiling? Open joists, or covered with gypsum board? If open joists, and a hot climate, I'd add a coat of radiant barrier paint first, to cut down on heat transfer, and then go with a 1500-1800 CFM fan.

[crabo]

650 cfm is a medium sized 4 bbl carbeurator.
c'mon craig :lol: just put a holley up there and open it wide.

one of those rotor twirly gigs should vent for you easily enough.

Good ideas, a 1250 Dominator should work fine. The turbine vents aren't doing it.

This is what I am thinking about doing.

http://www.tractorsupply.com/maxxair-heavy-duty-exhaust-fan-with-integrated-shutter-14-in-blade-3240617#product_tabs

or

http://www.tractorsupply.com/maxxair-heavy-duty-exhaust-fan-with-integrated-shutter-18-in-blade-3240609#product_tabs

The radiant barrier idea is worth checking out. I sheet rocked the walls, but not the ceiling. I really don't want to do that much work.

Here's a good link for figuring cfm. I was hoping by posting here, I would get some good ideas. I just need to go dig through the hot rod stuff and see if I have any old carbs left.

http://www.ehow.com/how_5771556_figure-attic-exhaust-fan-size.html

[geargnasher]

I see the problem, you're running that 50K BTU heater on full blast!! :kidding:

I'd build a cupolo about three feet square, put screened gable vents in both ends, and install a 20" box fan in the cupola blowing straight up. Unless you insulate between the rafters, or at least nail up foil-backed foam sheets, your best bet is to pull "cool" air from BOTH ends and out the middle of the ridge.

Gear

[bearcove]

Put in an insulated ceiling.

[tonyjones]

A rule of thumb in industrial warehouse ventilation is 6 air changes per hour. 10 would be better but not so much that you will feel the air movement. Calculate the area including the gable x 6 or 10 and you have the volume of air to be moved. When you size the louver(s) remember that the free area of a louver is typically about 50%. If the louvers are for inlet (supply) air and the fan for exhaust go a bit oversize on the louver area because if the air velocity through the louver is too high you will suck in water with the make-up air when it rains.

I hope this helps.

Regards,

Tony

[gwpercle]

The calculations you refer to are correct for calculating the required cfm's for an inclosed attic space. But I believe you want to ventilate the garage space and the open attic space above it. The rule of thumb I use is 1.5 cfm x 650 ( garage area ) = 1075 cfm's this would be absolute minimum for ventilation only.
Now if you plan to work in the garage and want to have a little air flowing through then double it 2 x 1075 = 2250 cfm's. So the 1400 cfm fan would be OK for general ventilation the 3, 000 cfm fan would do better for cooling the garage. Be sure to have at least one window or louver to open , opposite of the exhaust fan so you can get some fresh-air/cross ventilation . If you have an open garage door with an exhaust fan located above it the fan pulls air in thru the open door , sucks it up then out...it doesn't get to the back of the garage and it will be hot back there.
What I'm trying to say is fan cfm,s are important but the location(s) of the fan and intake openings are probably more important

[crabo]

The fan would have to go above the garage door because of the large window on the other end. The window opens about 2x6 ft in the opposite end.

[Charley]

Radiant barriers are great in hot climates. Down here in South Texas, an attic space with standard OSB decking can easily hit 160F in the summer. Add a decent radiant barrier, and temps drop to about 125F or so, and when the heat load is gone (clouds, sunset) the attic temp drops to ambient temperature in about 20-30 minutes, depending on ventilation.
Foaming the roof decking will work as well, but it is considerably more expensive, and in wet/damp climates, roof decking can have problems with mildew/mold/wood rot.

[GabbyM]

If it's an attic I’d use a vent-a -ridge and static gable vents.

Then a whole house ceiling mount fan in the garage to blow the attic clear and vent the garage. If your garage doesn’t have a ceiling mount a roof mounted fan.

[a.squibload]

If noise is important remember that smaller diameter fans (fast rpm) will be louder
than larger diameter (slow) fans.

I put a screened gable vent with rain louvers between the studs years ago,
now I can't get to it to install the leftover box fan!
How did all that stuff get in the garage?
One of these days...

[gwpercle]

Crabo,

Just exactly what are you planning to do with this space.

I have a friend that has a garage he uses as a work shop by opening the garage door and placing a large movable box fan ( it's an old attic fan with hardware cloth grills he made a wood frame and put casters on bottom ) he puts the fan wherever it's needed to keep him cool.

I think if I had a better idea of what the end result should be I might be better able to offer suggestions. I am a professional building designer and have been
involved with renovation and construction projects since 1973.
Also photo's of all four walls would help planning.

Placing the fan above the garage door , while not the best location, would give some ventilation. And if there is a window on the other end that opens , that might just do it . To increase air flow through open winndow the garage door could be closed slightly.

Back in the good old days we put an attic fan in the hall and lots of windows.
Central heating and air conditioning is the absolute greatist invention of the 20th century if you live in Louisiana, the heat and humidity are brutal and I well remember my first feeling of an air conditioned room...I thought I had died and gone to heaven. Heaven had better be air conditioned and have a shooting range.

gary

[crabo]

The garage is basically a workshop for casting, and projects. I thinking about a tube that would extend 6-8 feet behind the fan so it would pull air from the middle of the room instead of right over the door.

I had cobra vent put in the house, but didn't want it for the garage for when I want to heat it. Post 5 shows the window on the other end. It opens about 2 feet.

I also use an industrial fan that follows me where ever I am working. It's bad when its over 100 outside and you walk in the garage and it is even hotter.

[gwpercle]

The tube is probably a very good idea...cost effective too.

When its 100 degrees outside there isn't much you can do...bringing 100 degree air inside don't cool nothing...thats why attic fans were outmoded by central air conditioning. Something you might look into is a portable room cooling unit, its sorta like the portable fan, only it generates cooled air and blows it on you or in the room. Here in La. our power goes out during hurricanes, and it's usually summer. the units have started popping up for use with an electrical generator, the whole house unit may be down but 1 room can be cooled for sleeping.
You can just plug them into a 110 volt receptacle if you got power and they exaust hot air through a long flexible tube that you push out a window, then the cooling unit can be located in the room and moved around as needed.
My loading area is not heated or cooled either. What I did was get a Lee hand press and move my operation inside the house when needed. Can't cast in the house but winter isn't bad for standing over a hot pot out there.

gary