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Old 09-05-2008, 10:07 PM   #1
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Ridge vent plus what??


Ok... here's the situation. We are building a 25x50x18 (walls are 14') metal building, which will have a full ridge vent. Someone is trying to sell us a 36" exhaust fan w/ intake louvers, but from what I've read, this will work against the ridge vent. Should we ditch the exhaust fan and use soffit vents... are they installed the same on a steel frame as on a wood frame?

I read somewhere of a concern with snow buildup... no problem here, our concern is extreme heat and humidity. We need the most effective form of ventilation. Advice from anyone is appreciated!

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Old 09-05-2008, 11:28 PM   #2
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Ridge vent plus what??


I'm assuming you are insulating then.

Sounds like a pole barn. First thing we gotta know is it going to be perlins or rafters? If it's perlins then the ridge vent will do you no good and you are wasting your money on it since there is no flowage through from your soffits to your ridge anyways. If there is going to be no lid (ceiling) and you want ventilation then a powered gable vent on the south side and passive inlet on the opposite gable are what you want.

If it is rafters then proper soffit and continuous ridge vent is the way you want to go. You are correct that the two systems combined will negate each other.


Last edited by OldNBroken; 09-05-2008 at 11:30 PM.
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Old 09-06-2008, 01:04 AM   #3
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Ridge vent plus what??


Yes it's a pole barn, and we're using perlins. Now why wouldn't a metal bldg supplier tell us the ridge vent is useless?... sheesh

Yes, we're insulating with foam foil radiant barrier, which brings me to another question. Is it necessary to create a space of an inch or more between the foil and the underside of the roof? We were told it would hang slightly just from gravity (except for where it is fastened to the perlins), but i'm not sure that's true.

There will be no ceiling... insulation and perlins against the roof. Here's the exhaust fan we bought (but could easily return)...

http://www.grainger.com/Grainger/wwg...ryString=1hlb5

Now we're questioning whether this fan (and corresponding intake) is the way to create the most ventilation. Frankly, we don't understand the significance of all the specs and went on the advice of a sales rep. What do you think? Seems pricey too, $700 for fan/intake/thermostat...
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Old 09-06-2008, 07:53 AM   #4
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Ridge vent plus what??


I don't know what you are doing with the building but if you want just ventilation then the louver fan is good. If it is for comfort while working in this building take that fan back and buy for the same money 2 or more 36" portable barrel fans. I used to work in a building like that and it is hot. Gable mount is not that great.
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Old 09-06-2008, 10:21 AM   #5
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Ridge vent plus what??


I can see how the portable fans would be better when we're in there, but we won't be in the building that often, it's mostly for storage.

We need to keep the temp below 80 all the time (which is not easy in the south), so we thought a gable fan with a thermostat would keep a constant temp. You say gable mount is not that great... do you recommend any other option for keeping a constant temp (besides a/c)? The only two systems of ventilation we know of are ridge & soffit(not an option with perlins), or gable-mount exhaust fan/intake.
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Old 09-06-2008, 12:09 PM   #6
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Ridge vent plus what??


The insulation you are installing is more of a vapor barrier than any real insulation and the salesman just doesn't know much about proper ventilation which is why he is selling you a ridge vent.

The reason your gable setup seems so pricey is because you got it at Graingers. They have been around for decades and have always carried top quality products, but never bottom dollar. Am sure what you got from them will perform for years to come. If you want cheap, that's what the bigbox stores are for.

I'm afraid you are confusing ventilation with temperature control. They are two completely different animals. The best ventilation is going to give you (without a well insulated structure) is to keep your bldg at or above the ambient temperature at the time. If you are looking to keep it 80 degrees or cooler on a 100 degree day, I'm not sure you can accomplish that without insulation and temperature control. Ventilation has nothing to do with it. You could, as Tazin said, run the floor fans to circulate and exhaust air inside the bldg while the temperature outside is over 80 degrees. Short of insulation and a/c this would be most effective.
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Old 09-06-2008, 07:39 PM   #7
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Ridge vent plus what??


ok, thanks. Nice to know the exhaust fan will last, I guess we'll stick with that one. So our next step is to exchange the ridge vent (if possible) for a ridge cap, right?

We plan to set a thermostat on the gable fan/louver to turn on at 85-90%. Even though ventilation doesn't equal temp. control, do you think the gable fan will do a well enough job to keep the temp down in there most of the time? I just don't see what other choice we have.

As far as the radiant barrier, I realize it's not standard insulation, but will it reflect a lot of heat as expected? As you can tell, I'm confused about ventilation/conduction/convection, etc... not very good at physics.

But overall, do you think 1/4 inch foam foil insulation and the gable fan with opposite louver intake will provide enough ventilation to keep the heat down?
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Old 09-06-2008, 10:24 PM   #8
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Ridge vent plus what??


Yes, you just want regular ridge cap, the vented ridge is going to do you no good. As far as "will it work?", can't answer that. That all depends on the particular weather on the particular day in your area. I can only tell you it will do something. Whether that something is adequate, you are going to have to wait and see.

Like I said before, short of proper insulation around the whole structure and a temperature control system, you are at the mercy of mother nature for the most part.

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