Ridgevent vs. electric vent

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Old 07-15-04, 01:30 PM
cheechee
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Question Ridgevent vs. electric vent

We are replacing our roof and have to decide between ridgevents and an electric fan type vent. Does anyone know which is better?
Thanks,
Cheechee
 
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Old 07-15-04, 01:33 PM
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For sure the power vent fans they will pay you back. make sure you have vents in the over hang also and air can get up from them.


ED
 
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Old 07-15-04, 02:40 PM
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Hard to say!

Cheechee,

There is not enough info. to answer definitively. In order for roof ventilation to work properly, It must be balanced.

You need 1 Sq. Ft. of passive ventilation per 150 Sq. Ft. of attic space.
1/2 should be intake (low - as in soffits). 1/2 should be exhaust (high - as in turbines or ridge or gabels etc).

If you are using power ventilation, it must move at least .7 CFM of air per Sq. Ft. of attic space. It also needs .5 Sq. Ft. of intake area per 150 Sq. Ft. of attic.

You should NOT mix different types of exhaust!

This means that if you already have gabel vents, neither of the two proposed options may be correct. (Some exceptions)

Tell us how big the space is and what you have now and we could make a better informed suggestion.

Hope this isn't confusing!
 
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Old 07-15-04, 11:16 PM
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If you use power vents, just make sure to check to see if they are working.
I can't tell you how many roofs I've been on that the power vents weren't working.
 
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Old 07-16-04, 08:35 AM
cheechee
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Ed, Inky and Delirious,
Thanks for your replies. Inky, you asked for more information. We have 1200 sq. ft. of attic with soffit vents, 5 mushroom vents, and an electric vent that does not work. One roofer said we should add 7 more mushroom vents and put in a new electric vent. Another one recommended the extra mushroom vents also, but with ridgevents instead of the electric one. He said that if you have and electric vent along with other vents, that the air will follow the path of least resistance and you could be pulling air from mushroom vents instead of the soffits, or from the trap door even. This sounds like what you said, Inky, about mixing types of vents. Are you saying that if you use an electric vent you shouldn't have any other vents at all including mushroom vents? If this is the case, since we already have 5 mushroom vents, it would make more sense to use ridgevents, right? I like the idea passive venting. After all, in the 9 years we've lived here, we never noticed that our electric vent wasn't working.
Cheechee
 
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Old 07-16-04, 11:05 AM
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Cheechee,

I personally am not fond of the mushroom vents (I think they are ugly and they create more roof penetrations that could someday leak). If it were me, I would get rid of the mushrooms and the electric vent. It won't take much work to sheath over the holes while the old roof is torn off (assuming you're tearing off... and you should!). I would go with continuous ridge vent (provided you have at least 30 ft of ridge) with a 1" cutout on each side of the ridge beam. The ridge vent is relatively inexpensive and comes in many types. Many people prefer the "shingle-over" type because it blends in well with the rest of the roof (assuming you are using asphalt). Make sure there is a clear air channel from the soffits to the ridge.

The roofer that told you about the "path of least resistance" was correct. That is why you don't mix exhaust types.

All that having been said... the passive ventilation does not tend to keep the attic space as cool on a hot and sunny day. If it is properly sized, though, it does provide adequate ventilation to prevent ice damming, extend the life of asphalt and wood shingles, and allow humidity to escape.

There are as many different oppinions on attic ventilation as there are types of vents, roofing materials and climates combined.

If you decide to stay with the mushrooms, you probably need a total of 7 to 10 of them depending on their size. They should be evenly distributed along the roof near the ridge.

If you decide to go with power ventilation, You vill need one that moves at least 840 CFM of air. You will also need to keep it in good working order.

I hope this helps!
 
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