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Old 06-08-2010, 05:02 PM   #16
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71* outside 101* in attic


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Originally Posted by turbomangt View Post
I thought that you should NOT install an attic fan with ridge vents, I hate it when pro's have conflicting opinions...LOL!!!!!!!!!!!!!
IMHO, ideally, you should close the ridge vents so that your attic fan can rely on intake from the soffits only. But, if you close the ridge vent, then how does the warm air escape from the attic during the winter, especially if you have a furnace in your attic (most newer 2 zone homes have this).

The pulling power of attic fans are so much more effective compared to relying on the natural convection of the hot air inside the attic that even if you draw air into the attic from the ridge vent, you are still moving air faster.

Almost everyone that I've spoken to who's been in an attic with a fan and without a fan will tell you that the attic with the fan is much cooler.

Keep in mind that a ridge vent's effectiveness also relies on wind speed to pull out hot air.

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There is no way he can cool the attic below the outside temperature unless the fans are sucking conditioned air from inside the house. That sounds like a bunch of BS to me.
No, you misread what I wrote.

What I'm saying is that his A/C unit can now cool the 2nd floor of his home down to 71F now that there's less heat building up in his attic/transferring into his 2nd floor since it's being evacuated from his attic faster.

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Old 06-08-2010, 05:11 PM   #17
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71* outside 101* in attic


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Originally Posted by handy man88 View Post
IMHO, ideally, you should close the ridge vents so that your attic fan can rely on intake from the soffits only. But, if you close the ridge vent, 1)then how does the warm air escape from the attic during the winter, especially if you have a furnace in your attic (most newer 2 zone homes have this).

2)The pulling power of attic fans are so much more effective compared to relying on the natural convection of the hot air inside the attic that even if you draw air into the attic from the ridge vent, you are still moving air faster.

3)Almost everyone that I've spoken to who's been in an attic with a fan and without a fan will tell you that the attic with the fan is much cooler.

4)Keep in mind that a ridge vent's effectiveness also relies on wind speed to pull out hot air.

1)Why would you want the warm air to escape in the winter?

2)Attic fans often de-pressurize the attic, causing conditioned air to be sucked from the living space.

3)See #2.

4) no it doesn't.

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No, you misread what I wrote.

What I'm saying is that his A/C unit can now cool the 2nd floor of his home down to 71F now that there's less heat building up in his attic/transferring into his 2nd floor since it's being evacuated from his attic faster.
Aha - I did miss-read. But he could have achieved the same thing by adding insulation and air-sealing and would get the same benefit in the winter. Attic fans typically treat the symptom, not the disease.
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Old 06-08-2010, 07:10 PM   #18
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71* outside 101* in attic


My 2 worth: On my own home, 1900 ft., I have tried a few things over the years to keep the attic area cooler. I do realize that here in S. GA. this is a challenge. I do have two gable vents, I did have two power roof ventilators but determined that they were useless and removed them when they went out. Neighbors had installed ridge vents and declared them wasted monies. Going back to my industrial ventilation training, albeit poor, I obtained a squirrel-cage type circulation fan from an old A/C unit and mounted it right smack-dab in the middle of my attic about 18" from the peak of the roof. I then ran flex-hose to the gable on the east side (the cooler side) and made a transition for the flex hose to the triangular gable vent. Now when the temp reaches, supposedly 130 at the point of my thermal switch, the fan comes on, pulls air from the middle of the attic via the soffit vents. I had a remote thermometer up there for a few months to record temps and there was a significant difference in lower temps in the summer from the previous year. It just takes thinking and time to do what is needed. David
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Old 06-08-2010, 07:34 PM   #19
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71* outside 101* in attic


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How hot can an attic get before it starts cooking the shingles? I'm guessing that 101 is not too hot based on the suggested setting of 105 on the powered gable fan I installed. There is some controversy among pros about attic ventilation but most agree that the soffit and ridge vent combo is the way to go.
Approximately 168* for the asphalt to start to chemically degrade the molecules. I'm shooting from memory on a physics study i read, butthat is real darn close. Then, for each degree additional, exponential damage begins to occur.

Your fan motor will burn out quickly at that low of a setting in most regions.

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Old 06-08-2010, 07:52 PM   #20
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71* outside 101* in attic


http://www.dca.state.fl.us/FBC/publi...eportFinal.pdf

"As shown by Parker (1998 and 2000), decking temperatures show much larger increases to temperature with reduced ventilation (the data from Parker (2000) showed an average increase in the decking temperature of 3.7F during summer).

Thus, the average increase in shingle temperature may be much higher than the upper surface measured value. As demonstrated in the 1888 by Svante August Arrhenius, fundamental chemical molecular activity essentially doubles for every 18F of increase in temperature. As shingle degradation is large a function of oxidation, the rates of this decomposition can be expected to follow the laws of chemical reactions. Accordingly, if the average shingle temperature was elevated by 2F, the shingle life expectancy might be reduced by 11%."


http://www.resercon.com/Ventilation.html

Though the cold roof cost more to install, the difference is that of instead of your roof only lasting 15 years, it will last 30 to 40.


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Old 06-08-2010, 08:39 PM   #21
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71* outside 101* in attic


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1)Why would you want the warm air to escape in the winter?
To help prevent ice damming.

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2)Attic fans often de-pressurize the attic, causing conditioned air to be sucked from the living space.

3)See #2.
Unless you have properly sized soffits.

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Originally Posted by seeyou View Post
2)4) no it doesn't.
Yes, it does. Wind moving over the newer design ridge vents causes lower pressure under the vent which draws out the air from the attic.



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Aha - I did miss-read. But he could have achieved the same thing by adding insulation and air-sealing and would get the same benefit in the winter. Attic fans typically treat the symptom, not the disease.
Yes, but his attic would still be hot, which supposedly causes premature wear of the sheathing and shingles.
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Old 06-09-2010, 02:54 AM   #22
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71* outside 101* in attic


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To help prevent ice damming.
Ice damming chances can be reduced by more/better insulation. Static vents including ridge vent are the superior venting choice to further reduce chances. But, static vents and power vents on the same roof typically don't perform properly.

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Unless you have properly sized soffits.
I'm guessing you mean "soffit vents". You're speaking perfect world scenarios which rarely exist. Most of the power vents I see are installed are either on houses with inadequate insulation, inadequate intake vent, or both. They are too often used as an easy "fix" to a problem the "fixer" doesn't fully understand.

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Yes, it does. Wind moving over the newer design ridge vents causes lower pressure under the vent which draws out the air from the attic.
You're speaking of one specific product that I'm not aware of, so I can't argue about it. I can think of probably 20 different ridge vent products. All of the one's that I'm familiar with work from the chimney effect. Warm air rises. They work fine on a still day. They might move more air on a windy day, but they are in no way dependent on wind to operate.

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Yes, but his attic would still be hot, which supposedly causes premature wear of the sheathing and shingles.
And I didn't say not to vent the attic in question, but instead to treat the disease, not the symptom. It was hot in the upstairs because too much heat was getting through the ceiling from the attic. Your neighbor's solution was to use more electricity. It worked. But, his solution does nothing to keep the space warmer in winter or to keep the meter from spinning.

edit: Oh yeah - There are a lot of roofs that aren't asphalt shingles. I've been roofing for 25 years and we seldom do asphalt shingle roofs. And, the shingle manufacturers that I'm familiar with allow their product to be used on insulated (non-vented) roof decks.
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Old 06-09-2010, 11:43 AM   #23
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71* outside 101* in attic


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edit: Oh yeah - There are a lot of roofs that aren't asphalt shingles. I've been roofing for 25 years and we seldom do asphalt shingle roofs. And, the shingle manufacturers that I'm familiar with allow their product to be used on insulated (non-vented) roof decks.

With a limited 10 year warranty if things have not recently changed, at least in regards to Certainteeds limitations.

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Old 06-09-2010, 12:09 PM   #24
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71* outside 101* in attic


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With a limited 10 year warranty if things have not recently changed, at least in regards to Certainteeds limitations.

Ed
I'll have to go back and look, but IIRC, that's the coverage for over an un-vented attic. Insulated roof decks have full coverage, provided they're one of the CT "approved" systems.

Edit: I went back and looked and the way I read the warranty is if prevailing building codes are met, the full warranty is in effect. You might interpret it differently. So, if foam on the bottom of the sheathing is allowed by code, as long as the proper sheathing is used, the warranty should be good.

Last edited by seeyou; 06-09-2010 at 12:15 PM.
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Old 06-09-2010, 04:00 PM   #25
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71* outside 101* in attic


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Ice damming chances can be reduced by more/better insulation. Static vents including ridge vent are the superior venting choice to further reduce chances. But, static vents and power vents on the same roof typically don't perform properly.
Again, better insulation won't help newer homes these days that have multiple zones that result in the furnace being located in the attic along with the gas flues that go through the attic.

Static vents and power vents on the same roof don't perform as ideally as a standalone power vent sans static vents, but as I said, they do pull air out of the attic faster.

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I'm guessing you mean "soffit vents". You're speaking perfect world scenarios which rarely exist. Most of the power vents I see are installed are either on houses with inadequate insulation, inadequate intake vent, or both. They are too often used as an easy "fix" to a problem the "fixer" doesn't fully understand.
If this easy fix works, then the fixer doesn't complain.

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You're speaking of one specific product that I'm not aware of, so I can't argue about it. I can think of probably 20 different ridge vent products. All of the one's that I'm familiar with work from the chimney effect. Warm air rises. They work fine on a still day. They might move more air on a windy day, but they are in no way dependent on wind to operate.
Chimney effect is very slow as it does not evacuate hot air as fast.

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And I didn't say not to vent the attic in question, but instead to treat the disease, not the symptom. It was hot in the upstairs because too much heat was getting through the ceiling from the attic. Your neighbor's solution was to use more electricity. It worked. But, his solution does nothing to keep the space warmer in winter or to keep the meter from spinning.
I agree, but I'm not sure he cares that he's spending more money on the sympton vice the disease.

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edit: Oh yeah - There are a lot of roofs that aren't asphalt shingles. I've been roofing for 25 years and we seldom do asphalt shingle roofs. And, the shingle manufacturers that I'm familiar with allow their product to be used on insulated (non-vented) roof decks.
That really depends on what part of the country you live in. In Southern CA, they go with clay tile. In the midatlantic to northeast, it's mostly asphalt shingle.
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Old 06-12-2010, 05:21 PM   #26
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71* outside 101* in attic


Hi

Without getting to bogged down, the problem that you have is related to radiant heat transfer. The best example is a south facing window, radiation from the sun travels through the glass and gets absorbed into the structure of the building and furniture and fittings, because the energy is absorbed it warms up the fabric of the building and in doing so loses some of its energy and no longer has sufficient energy to escape out of the window and becomes trapped and warms the room your loft space is no different, just that the maximum amount of energy passing into the loft should be slightly less.

Ventilation may help, but you would need so much of it, you would have to think about opening up most of the roof, a less drastic option would be to add a signficant amount of insulation in the loft space, between and or over the rafters - your looking at around a 4" thickness of PIR or Polystyrene Insulation to make any significant difference.

As a rule you would need to leave at least a 2" gap between the roof covering and the insulation, then it depends on the depth of the rafters and how much space you have left to fill with insulation material. For example, if you have 4" rafters you should consider 2" of insulation between and 2" over the face of the rafters, however, if you have 6" rafters you could put 4" of insulation between the rafters. Only problem, timber is not really as good an insulating material as some people may believe - compared to PIR or Polystyrene timber is 70 times less efficient insulating material. Timber loses heat at around 1.5W/m2C whereas PIR loses around 0.024W/m2C. Once you have some insulation in place you may find it affordable to put in a small ac unit (assuming you wish to use the space?)

I hope the above is of some help.

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Old 06-12-2010, 07:11 PM   #27
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71* outside 101* in attic


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a pleasent day of 71* my attic is cooking at *101
I don't guess you're in FL?

http://www.dca.state.fl.us/FBC/commi...CR-1496-05.pdf

These guys really did their homework, 49 pages worth.

Last edited by Yoyizit; 06-12-2010 at 07:24 PM.
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Old 06-14-2010, 09:35 AM   #28
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71* outside 101* in attic


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The sun is warming up the roof and that heat is transferring through the sheathing and warming the attic.

Not unusual at all to see temperature differentials like that. If it was 30 degrees and sunny outside, it'll probably be 70 degrees in the attic.

The main purpose of venting an attic is to remove moisture. It should reduce the heat differential some, but not completely. If the attic was not vented, the temperature would probably be 120 on a 70 degree sunny day.
The attic in my home is always so much hotter than the rest of my home. If it was actually cold up there I'd be worried about how much my bills were going to be from the AC cooling the attic.
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Old 06-14-2010, 11:06 AM   #29
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I thought that you should NOT install an attic fan with ridge vents, I hate it when pro's have conflicting opinions...LOL!!!!!!!!!!!!!
I notice this from time to time too. Wonder why Pros never post their work pics. I bet other pros will dissagree a lot.
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Old 06-14-2010, 01:20 PM   #30
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I notice this from time to time too. Wonder why Pros never post their work pics. I bet other pros will dissagree a lot.
Respectfully, members should refrain from making such "Blanket" comments or accusations such as this.

If you would have been around and checked your facts first, you would find out that many of the well respected regulars here have on many occasions posted our own work photos which pertain to a particular topic.

Other times, rather than rely on our photos, we provide a link to a respected source or repeat the sources contents verbatim to the best of our ability and time we have available to donate our time and knowledge for free to assist others in their concerns.

Ed

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