Adding small fan to passive attic vent.


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Old 04-05-09, 06:09 PM
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Adding small fan to passive attic vent.

I have a condo on the second floor of a 2 story building, above me is an attic. I've been insulating the attic in an attempt to not only cut down on energy usage, but to stop from having to use the AC so often in the Summer (it's annoying).

The attic has soffit vents and two 10" passive vents on the roof, no ridge vent (I've bene pushing for one, but it's not going to happen since we just got a new roof a year ago).

Since the attic is "common space" I can't make any big changes (such as a mushroom fan thru the roof) but I could add one of those temperature controlled fans to one or both of the 10" vents that are already there.

Would a fan like that help get the hot air out of the attic, or is it just wasting time and energy?
 
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Old 04-05-09, 08:03 PM
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In my opinion they help a lot. Attics with passive venting require a lot of vent area and even at that they are slow. I run mine on a switch where I can shut it off/on/or auto. I just like switches. In your case it sounds like you have a lot of attic to vent, but they will get rid of the heat from the day and allow you to enjoy some of the cool from the night

Bud
 
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Old 04-05-09, 08:44 PM
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The attic is about 800 square foot (28'X29'). The peak is about 9 foot high.

Do you have any recommendations for a fan that will work in my 10" passive vents? Will the fan hinder the natural airflow when it is shut off?
 
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Old 04-06-09, 06:12 AM
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The natural air flow is so slow I don't think the fan assembly will affect it. If there are no side walls, then your volume is about 3,600 cubic feet. However, just pointing an exhaust fan at a gable vent will be very inefficient, even with the shroud they provide. But anything will be much better than nothing. Fans are rated in cubic feet per minute and you are more concerned about hours, so anything in the 2,000 to 4,000 cfm will work. I'm guessing as I don't know what volume will actually make it out through the gable vent.

Bud
 
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Old 06-05-09, 08:51 PM
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Hell, I haven't been able to find any type of fan made for this purpose.

Would it help if I just made a square shroud out of sheetmetal and attached a fan to it, then installed the shroud over the 10" opening in the plywood roof?
 
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Old 06-05-09, 09:27 PM
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As I'm sitting doing nothing, unlike Bud, yes that will help. Seal your attic/house holes, and here is how to figure the NFA:

Attic Ventilation

BlockTheHeat.com -Attic Ventilation Problems Be safe, G
 
 

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