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Old 04-29-2010, 01:33 PM   #1
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Thinking of adding powered roof vents.


Hello all,
I have a two story home in Orlando FL. I am having the roof replaced with a complete tear off, and re roof with 30 year architectural shingles. Currently there are approx. 176' of soffet vent and 10' of ridge vent due to a hip roof. I plan to extend the ridge vent about 2 feet.

  • Would it be advisable to add 2 or more of the Master Flow Power Roof Mount Vent 1250 CFM's powered roof vents in this situation?
  • What other ventilation options would be better?
  • If I add the powered roof vent should I remove the Ridge vent all together?
Thank you in advance for your help.

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Old 04-29-2010, 03:57 PM   #2
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Thinking of adding powered roof vents.


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should I remove the Ridge vent all together?
"Ridge vents advertise openings of 12 to 20 square inches per linear foot. Converting, 20 si = 0.139 sf x 60' =8.33 sf for the entire ridge. That is nearly four times the area of the 3 turbine vents!"

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Old 04-29-2010, 04:52 PM   #3
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Thinking of adding powered roof vents.


Quote:
Originally Posted by Yoyizit View Post
"Ridge vents advertise openings of 12 to 20 square inches per linear foot. Converting, 20 si = 0.139 sf x 60' =8.33 sf for the entire ridge. That is nearly four times the area of the 3 turbine vents!"
This may or may not be the correct measurement I have not done the math, but the theory behind turbines is they create convection that pulls hot air out when they're spinning.
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Old 04-29-2010, 05:09 PM   #4
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Thinking of adding powered roof vents.


Somewhere online is the CFM you typically get with ridge vents and with turbine vents and powered vents.

Disregarding appearance, there is a payback period determined by the cost of the initial installation vs. how long it takes to recoup your investment based on energy savings and energy costs in your area. This correlates well to the before and after attic temperatures.

With these [impartial?] numbers it should be easy to pick clear winners and clear losers. Don't listen to what manuf's say.

Last edited by Yoyizit; 04-29-2010 at 05:12 PM.
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Old 04-29-2010, 05:14 PM   #5
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Thinking of adding powered roof vents.


Quote:
Originally Posted by Yoyizit View Post
"Ridge vents advertise openings of 12 to 20 square inches per linear foot. Converting, 20 si = 0.139 sf x 60' =8.33 sf for the entire ridge. That is nearly four times the area of the 3 turbine vents!"
He's only got ten feet of ridge vent though... 1.5"x12" per foot x10 ft.=180" sq./144=1.25 sf nfva

That would accommodate 187.5 sf of attic floor space.
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Last edited by AaronB; 04-29-2010 at 05:17 PM. Reason: Did the calculations
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Old 04-29-2010, 05:17 PM   #6
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Thinking of adding powered roof vents.


Quote:
Originally Posted by AaronB View Post
He's only got ten feet of ridge vent though... 1.5"x12" per foot x10 ft.=180" sq./144=1.25 sf nfva

That would accommodate 187.5 sf of attic floor space.
I thought we need to know attic volume.

If you search this site for

3200

the first thread has a link to a study on this.

Here's another
http://www.deerparkroofing.com/ventilation.php
They seem credible.

The OP's particular shingles may have their own ground rules.

Last edited by Yoyizit; 04-29-2010 at 05:29 PM.
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Old 04-29-2010, 05:36 PM   #7
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Thinking of adding powered roof vents.


Thank you for your responses. I was not talking about turbines but Master Flow Power Roof Mount Vent 1250 CFM's powered roof vent. the attic square footage is approx 1925 sq ft.
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Old 05-02-2010, 08:17 AM   #8
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Thinking of adding powered roof vents.


Quote:
Originally Posted by budster View Post
Thank you for your responses. I was not talking about turbines but Master Flow Power Roof Mount Vent 1250 CFM's powered roof vent. the attic square footage is approx 1925 sq ft.
If you don't have enough inlet to supply replacement air for power vents they will depressurize the attic. If the attic is not properly air sealed, this will draw conditioned air from the living space. I exhaust all non-powered options before installing a power vent unless there is more than adequate OPEN inlet to supply them. Powered vents have a limited lifespan and use a fair amount of electricity to operate. It might be more advantageous to add insulation.

And yes, I'd do away with the ridge vent if you add the powered vents.
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Old 05-02-2010, 12:22 PM   #9
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Thinking of adding powered roof vents.


I have 176' of continuous soffet vent, there are insulation baffles. So incoming air is not a problem. I need to increase my exhaust size.
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Old 05-02-2010, 12:54 PM   #10
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Thinking of adding powered roof vents.


You have heat in your attic, and you are trying to address the problem. Since you are tearing off the roof already, you have the opportunity to really deal with your issue.

Since you are going down to your roof deck, look at insulating at the deck surface by adding a few inches of rigid foam board, then topping that with a radiant barrier deck. You can stop the heat before it gets anywhere near your living space. Plus, the foam board is waterproof, giving you an additional waterproof plane under your roof deck.

Don't mix a power ventalator with a ridge vent.
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Old 05-02-2010, 12:58 PM   #11
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Thinking of adding powered roof vents.


Also, if you add insulation up to the new insulation standards of your area (mine is R30) you get a federal 15% tax break on it. Same goes for the shingles if they are Energy Star approved. Has to be bought in 2010 though.
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Old 05-02-2010, 01:05 PM   #12
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Thinking of adding powered roof vents.


Quote:
Originally Posted by budster View Post
I have 176' of continuous soffet vent, there are insulation baffles. So incoming air is not a problem. I need to increase my exhaust size.
That's 132 sq ft of inlet at best. Probably only an effective square footage of about 100 ft sq which is way more than adequate. About 7 sq ft of exhaust vent for static vents should be adequate which is a lot of button vents. I'm not a big fan of powered vents, but from the info you've given, they might be your best option.
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Old 05-02-2010, 02:27 PM   #13
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Thinking of adding powered roof vents.


How wide are the soffit vents?

With 1925 sq ft of attic floor, you will need 13 square feet of nfva on intake, and exhaust. That is 37 mushroom vents, 99 feet of ridge vent, 3 12" turbines, 2 14" turbines, 3 solar powered exhaust vents, or two powered exhaust vents, along with 1872 sq in. of intake to properly vent your roof.

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