Help with Attic Exhaust

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I'd love to. Unfortunately, I'm in South Florida. Finding an honest contractor would be about as easy as finding WMDs in Iraq!
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Lost-In-Translation wrote:

Good point.
--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math
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wrote:

You can get any color or material you want in CT. My roofing is light gray asphalt shingles. One neighbor has a tan asphalt roof and another neighbor has a green, metal, standing seam roof. There are several homes in my area with Spanish style red clay tile roofs, not to mention the many who have slate or cedar shingle roofs.
BB
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On Wed, 02 Jun 2004 18:01:31 GMT, "Lost-In-Translation"

I think you are trying to keep it overly cool in the attic. Most of these type fans are set to come on at 120 degrees. On mine I did block the vent with plastic on the end of the house with the fan. Fan generally comes on around noon and cuts off right around sunset.
Steve B.
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I'm not an engineer, but did you do some basic calculations to determine how much volume of space is in your attic. Exhaust fans are usually rated in cubic feet per minute (CFM). How many cubic feet of space is in your attic? A small gable fan will not move as much air as a whole house fan. My guess is that your fan is too small to move the amount of air out of the attic necessary to bring it down to a satisfactory temperature. Other factors also come into play such as the amount of sunlight hitting your roof and the amount of insulation you have.
Keep in mind that you will never get it cooler than the outside air that you are sucking in.
Don't seal off your soffit vents. The make up air needs to come from somewhere.
I find it difficult to believe that the outside air is hotter than the air in the attic.
John Grabowski http://www.mrelectrician.tv
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Lost-In-Translation wrote:

And what did you expect it to do?
The sun on the room normally makes the air in the attic a lot hotter than outside. Passive ventilation (your gable vents along with the soffit vents) bring cooler (but still hot) air from the outside through the soffit vents and lets the hotter air out the gable vents (hot air rises).
Adding a fan usually increases the air flow. Occasionally it may acturally decrease the air flow because of short-circuiting, but I tend to believe that is rare. Over all as long as the fan is working I believe almost all will help decrease the temperature. If the fan fails, which many do as most are cheaply made, it will reduce the air flow and usually cause increased heat.
My personal opinion (from personal experience) is that most of the time fans are not worth the effort.

Are you sure you mean "gable" and not "soffit?" Gables are at the top of the end wall and soffits are along the bottom edge of the roof.

And when you exhaust all the air, you have a vacuum. If you exhaust air out, it has to come in somewhere.
Not only that, without ventilation, you could collect moisture and end up with mold and water damage. You would also end up with a lot hotter attic since the sun on the roof is going to be adding a lot of heat with no place to go.

It brings in less hot air.

Leave the fan as it is or take it out. Make sure you have enough ventilation. Check the fan from time to time if you don't take it out. When it stops working take it out and don't replace it.
--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math
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Check the instruction booklet for the gable fan. It should indicate what size attic it's suited for and how many square inchs of air inlet it needs, ie soffit, other gables, to work properly. Make sure the fan is the right size and there are sufficient soffit vents. If the fan is too big, or there is not enough air inlet area, then you will suck up cool air from inside the house through random holes and openings.
Also, what is in front of the gable fan? Is it being blocked by fixed louvers or do you have movable ones that open? It's important to have as clear an opening for the fan as possible. Among fixed louvers, I've seen considerable variation in how they are designed and how much air they will let a fan push through.
Most houses could benefit from more soffit vents than what builders typically install. The best solution is a ridge vent combined with soffit vents, however I realize with a tile roof, that's probably out. I certainly wouldn't fool around with blocking off any soffit vents, as what you want is more air coming in, not less.
Even a 10 degree difference in attic temp is not all that bad. Say the attic was 110 without and 100 with. That means the temp delta between the attic and house at 70 was 40 and is now 30. That translates into roughly 25% less heat flow through the insulation into the attic.
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Chet Hayes wrote:

Yes, but. If the attic is insulated with R-30, only 3% of that 10 degree difference gets to the ceiling side of the insulation. (Thermal conductivity [U factor] = 1/30 = 3.3%).
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I think you would find the Building Science Corporation web site helpful. The information is from building researchers. Climate specific problems are addressed. I and other architects refer to it, if you want recommendations. Tom Baker
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Lost-In-Translation wrote:

First, I hope you have openings to let air into the attic when the fans are running, e.g., soffit vents or other gable openings. Second, you are right it will suck in the hot air, and the attic can never be cooler than the outside temperature. However, if the fan lowers the temperature in the attic to 10 degrees over the outside air temperature, it will significantly reduce heat buildup in the house.
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George E. Cawthon wrote:

Only if the attic is poorly insulated.
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Lost-In-Translation wrote:

R-30. Anything more than that gets into the law of diminishing returns. http://www.progress-energy.com/aboutenergy/learningctr/savingtips/rvalues.asp
You probably should just have some more loose fill (sounds like you currently have perlite) blown in. Laying bats over the top of loose fill is problematic because of the voids created in the process.
White tile is a good choice over any other color for a Florida roof since white's greater solar reflectivity means significantly lower temperatures for the roof deck (and therefore, it is probable that the underlayment will last longer). Of course, you have to clean the algae off it every so often....
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Bob in CT wrote:

I don't know how well they work but there are a number of sites with insulating covers you put in the attic above your fold down stairs. Here's one link.
http://www.batticdoor.com /
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I'm not sure if anyone else picked up on this, but what TIA bought was a gable end vent fan. The purpose of this device is to create a negative pressure inside the attic to draw outside air in through either OTHER gable end vents or soffit vents. By the way, what TIA is calling gable vents are really soffit vents (since the run the length of the home). Getting outside air into the attic helps keep the temps closer to the outside temp which is important in both the summer (keeps roofing from overheating and helps to stop it from warming living space) and winter (stops ice damming).
I suspect that what TIA REALLY wanted to buy was a whole-house-fan. This device is used to draw air out of the living space and into the attic where it can be vented through either a ridge or gable vent. Of course, you have to open all your windows to make it work, and again you're still at the mercy of the outside temp. This is only effective during seasons when night time outside temps are much lower than in the inside (where daytime heat has built up). Eventually, in summertime, it's just too hot inside and out to do any good. I had one of these fans and it ran for maybe 20 days out of the whole year.
Bobby in NJ
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I'm not sure if anyone else picked up on this, but what TIA bought was a gable end vent fan. The purpose of this device is to create a negative pressure inside the attic to draw outside air in through either OTHER gable end vents or soffit vents. By the way, what TIA is calling gable vents are really soffit vents (since the run the length of the home). Getting outside air into the attic helps keep the temps closer to the outside temp which is important in both the summer (keeps roofing from overheating and helps to stop it from warming living space) and winter (stops ice damming).
I suspect that what TIA REALLY wanted to buy was a whole-house-fan. This device is used to draw air out of the living space and into the attic where it can be vented through either a ridge or gable vent. Of course, you have to open all your windows to make it work, and again you're still at the mercy of the outside temp. This is only effective during seasons when night time outside temps are much lower than in the inside (where daytime heat has built up). Eventually, in summertime, it's just too hot inside and out to do any good. I had one of these fans and it ran for maybe 20 days out of the whole year.
Bobby in NJ
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Dear Bobby in NJ
Thanks for weighing in on this.
Just for reference, TIA isn't a name, it's USENET speak for "Thanks in Advance"
Have a great weekend!

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Yes, Tia is a name, dumbass.
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Lost-In-Translation mighta wrote:. > Just for reference, TIA isn't a name, it's USENET speak for "Thanks in

reference, it means "aunt" in some languages, like Spanish... bitch! : ) That's like... my third emoticon, ever. Sorry. Tom Someday, it'll all be over....
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Not the way I used it . . .asshat!
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Well, I'm aware of TIA, IMHO, IIRC, and all that, but one usually signs a name to letters, posts, etc so we know who to address in replies.. TIA could have been your initials or a nickname.
Bobby
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