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Old 07-10-2012, 05:02 AM   #1
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ridge vent and or fan?


should you install a power fan when you are installing ridge vent on a new roof?

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Old 07-10-2012, 08:11 AM   #2
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ridge vent and or fan?


You don't in 99% of the cases.

The two systems are not usually used or specified in conjunction with one another because they wind up fouling things up.

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Old 07-10-2012, 04:20 PM   #3
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ridge vent and or fan?


Imagine a power fan kicks on and it starts to pull air. It can pull air from a 18 square inch per foot hole from the ridge vent 1 foot away, or it can pull air from a soffit that may be 20 feet away with a hole only 6 to 8 squares inches per foot.

The fan will pull air from the path of least resistance, which is the ridge vent. Causing the ridge vent to become and intake, which won't help keeping rain out.

What you describe is done all the time. Problem is the "Green Phd" types now hate power vents. Not only because they use power, but mostly because they are almost always installed incorrectly. So to keep things simple, most roofs shouldn't have a power fan.
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Old 07-10-2012, 05:43 PM   #4
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ridge vent and or fan?


I would have to disagree.

If installed correctly with adequate intake it is perfectly acceptable. I have installed powered attic fans with ridge vents and documented the results.

http://www.roofingcontractorreview.c...tic-space.html

http://www.roofingcontractorreview.c...ttic-Fans.html

If anyone can show me hard evidence to the contrary, I would be happy to review it.
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Old 07-10-2012, 08:57 PM   #5
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ridge vent and or fan?


Key word their being "installed correctly".

I really like the work you put into the the model houses on the ventilation videos. I applaud your work.

You state that "Both eaves are vented with net free area equal to or larger than the ridge vent."Typical ridge vent is 18 sqin per foot. Typical eave may be only 1/3 of that if continuous.

Your model is what I believe we should strive for in attic ventilation. Tons of intake at the soffit. The new 2012 IRC actually addresses the balance of air intake with the larger portion coming from the eaves.

I didn't check through your site but did you try to seal off the soffits of the model house and try to force air through by "short circuiting" it? Then did you try to find at what ratio of opening the soffit did you find air stop short circuiting?
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Old 07-11-2012, 05:59 PM   #6
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ridge vent and or fan?


Quote:
Originally Posted by dmc@RCR View Post
I would have to disagree.

If installed correctly with adequate intake it is perfectly acceptable. I have installed powered attic fans with ridge vents and documented the results.

http://www.roofingcontractorreview.c...tic-space.html

http://www.roofingcontractorreview.c...ttic-Fans.html

If anyone can show me hard evidence to the contrary, I would be happy to review it.
+1

I am liking the videos.

That being said, the first question I would ask is why bother?

Attic temperatures are largely irrelevant if the moisture is being handled properly. If the attic is properly insulated, the small bit of temperature offset that the fan will provide over a standard passive ridge vent/soffit combo is very slight and comes at the expense of the fan and the small amount of electricity to run it.
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Old 07-12-2012, 08:11 PM   #7
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ridge vent and or fan?


Quote:
I didn't check through your site but did you try to seal off the soffits of the model house and try to force air through by "short circuiting" it? Then did you try to find at what ratio of opening the soffit did you find air stop short circuiting?
Good questions. I have not had the time to try that and probably would need better testing/measuring tools.

Quote:
Attic temperatures are largely irrelevant if the moisture is being handled properly. If the attic is properly insulated, the small bit of temperature offset that the fan will provide over a standard passive ridge vent/soffit combo is very slight and comes at the expense of the fan and the small amount of electricity to run it.
There will always be houses that for some reason cannot be easily insulated or moisture controlled. And there is the small benefit to the roofing and sheathing.
The amount of airflow in an attic with ridge vent and soffit vents is minimal. I have video (not posted yet) of an attic with ridge, gable and soffit vents, where more air is exhausting from the gable vents than the ridge vent.
I believe the addition of an attic fan will reduce the temperature of an attic much more than you think.
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Old 07-13-2012, 05:58 AM   #8
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ridge vent and or fan?


Some attics are difficult and a PAV might be a band-aid for the short term, but when the roof is re-done, the insulation should be fixed.

If you have more than a 4:12, the amount of cooling that happens into the attic is so minimal than you can't even really quantify it in most cases.

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