Attic Fan - Yes or No?

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Old 04-24-18, 08:39 PM
J
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Attic Fan - Yes or No?

Situation is we're getting a new roof, and the current roof has a power ventilator fan. It's inoperable (no power even connected to it), but it's there. With getting the new roof, I need to decide a couple things: 1) whether to have a fan at all, and 2) whether to change from a power fan to a whirlybird.

Background is, the house has continuous soffits along front and back, and has/will have a full length ridge vent.

I see opinions saying fans are good (i.e., they help cool the attic), and opinions saying not good (i.e,, they mess with the natural air flow from soffit to ridge; they don't cool the attic because the heat comes from radiant heat, so they just replace hot air with hot air; they just suck conditioned air ($) out of the house). Also see advice not to mix ventilation systems (i.e., if you have soffits/ridge vent, don't have fans too.)

I would rather replace that part of the roof decking and not have a fan at all with the new roof. I'm believing the advice that it doesn't really cool the attic and just messes with the natural flow from soffit to ridge, and I would rather not have the roof penetration - it's just another possible leak spot. If changing to whirlybird, I don't think just one would even be enough to do anything, so would need to open up a couple additional holes for more whirlybirds, which I also obviously don't want to do.

One factor is that I am currently in the process of air sealing the attic, so I think that would prevent a power fan from just pulling conditioned air out of the house and into the attic, and might actually result in cooling, but I'm still thinking that just soffit and ridge venting only would be best.

So looking for some opinions. What would you do? Get rid of the fan or keep it?
 
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Old 04-24-18, 08:55 PM
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I would get rid of it and would also not add whirlybirds if you have ridge venting.
 
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Old 04-25-18, 06:53 AM
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Attics will get extra hot with no venting at all. With proper soffit and ridge venting plus your air sealing efforts in the attic (and lots of insulation to follow) you will be all set. There are several pieces of incorrect advice on your list but not relevant to the final selection. As X said, get rid of the broken fan while the new roof is going up.

Cooling an attic with ventilation is only necessary if you have insufficient insulation and even then the benefits are questionable.

One consideration for the new roof is to select a color and radiant reflective shingle that can reduce the amount of solar energy that ultimately enters the attic. There should be a good selection that offer reflectance properties.

Bud
 
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Old 04-25-18, 10:33 PM
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OK, great. Will go ahead with getting rid of the fan, and work on the attic sealing. And yes, I do need to beef up the insulation. I calculate I only have about 1/2 the depth of blown in fiberglass I should. Maybe it has settled over the years...

Is it alright to add cellulose over top of that? Or should I stick with like materials and add more fiberglass?
 
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Old 04-25-18, 10:51 PM
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Even with full soffit and ridge, make sure that the total free area of vent is adequate for the square footage of the attic. I'm sure it will be, but you need to check the free area (I think that's the right term) of the products to be sure.
 
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Old 04-28-18, 10:24 AM
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Thanks for mentioning that, Gunguy. Ran through a calculation, and yes, I have way more vent area than I would need.
 
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