Attic fan? Whole house fan? Neither? Both?

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Hello again!
I ran a search, and I am nor confused than ever, plus I have some other info from a contractor.
We have a 2 story, 2400 square foot "modern colonial" home (from what I am told). LOL
Here is a picture of the house for reference:
http://farm1.static.flickr.com/205/451169757_3a09fe48e7_o.jpg
Our attic is insulated, with blown-in insulation. There is no storage in the attic, and access is through a small access in our We have ridge vents on the roof, with no other ventilation for the attic. We were considering installing a whole house fan or maybe even an attic fan. Are either of these a better option than the other? We would like to lower the temperature of the house when it's cool outside (70-75 degrees) but warm inside (79-88 degrees).
I spoke with a friend who is a contractor. He seemed to thin an atic fan without gable vents would not be effective, and that a whole house fan would not give us the result we desire. Can anyone else inout on this?
If you need additional info, please let me know.
Thank you, Chris
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Hi,
Live in Mass., also a Colonial.
All I can tell you is that the attic fan we installed many years ago in the gable (belt driven) was probably the best thing we ever bought. We pull down the steps leading up to the attic, run the fan for 5 minutes, and all the hot summer air in the attic is gone. Works unbelievably well in cooling off the house.
W have louvres in the fan end end, but very uncertain if they are needed. Keep thinking attic ventillation from one screened end gable to this one would be much better if I removed them ? Not sure what function they actually provide ?
Anyone with any thoughts on this ?
Bob
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On Tue, 21 Jul 2009 04:35:15 -0700 (PDT), "Chris (SilverUnicorn)"

    Where do you live? Tell us a lot about the local weather including humidity. What do those in your area recommend and do.
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Chris (SilverUnicorn) wrote:

I would try a 20 inch box fan in an upstairs window. Fit it snugly and use it to exhaust air. Then open other windows. Close doors to rooms that you do not need to cool. A much cheaper way to try to cool the house. BTW I have done this and it works.
Lou
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I'm with him. First spend your money on the gable vents. Then on the attic fan. You will get some relief from an attic fan now-- and a little more if you open the door to the attic and use it to suck all the air through the house at night.
But the gable vents will act passively long before the thermostat on the attic vent kicks in.
Looking at the picture I'm guessing that we're looking more or less east. Are there good soffit vents and a ridge vent in that room over the garage? That's where I'd start- with whatever roof has a southern exposure. Do whatever you have to do to cool it off-- ventilate, insulate, spray water on it. . . .
Jim
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wrote:

How about a photo of the inside of the attic, You have to figure how much air can go up the attic entrance and size it right, with added gable vents how will it cool the area below, wont it just cool the attic? just size it all right by cfm I am guessing.
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Chris (SilverUnicorn) wrote:

You're thinking of sucking air in through a window or windows of the house, right? In that case, you also have to have an exit for the hot air. The ridge vent might suffice for a whole house fan assuming the vent area is great enough.
For an attic fan, you also would have to have a way for air to get from the lower house to the attic...opening a ceiling trap door would work but having to open and close it would be a nuisance. Basically, as I understand it, attic fans aren't meant to suck air from lower storeys but from the eaves thus cooling the attic. I'd want gable vents too for that. The cooling effect on the living area would depend largely on the effectiveness of the insulation between it and attic...effective insulation = little cooling.
When I was in college I had a railroad apartment - full width living room, hall from it to back, other rooms opening off the hall. Air conditioning was uncommon and it was hot so I put a window fan in the front window, opened one in the back. Worked well, nice breeze and the breeze was controllable simply by closing/opening a window where the breeze was wanted.
Almost 50 years later when we built a house I remembered how effective that window fan was and put in two "whole house" fans...one in the house, one in my shop. Both work very well but we never use the one in the house because of the noise. Lots of noise. Freight train type noise. The one in the shop I use a good bit because there is generally already a lot of noise and it helps get rid of wood particles in the air (it vents into a small, closed area with a gable vent in the attic)
In short, I'm thinking a couple of window fans might work better for you. .
--

dadiOH
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There have been significant improvements in quieting fan noise. The newer ones aren't nearly as bad.

I'd be a bit leery about blowing saw dust into an enclosed space without filtering it first. I'd also wonder about the dust building up on the motor and potentially overheating. Do you inspect/clean the fan often?
R
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RicodJour wrote:

Often no; from time to time, yes.
Very little accumulates, almost all is blown out the (largish) gable vent. From there it drifts around until it finally settles somewhere on our 10 acres. Once settled it decays trying futilely to enrich the sand that passes for soil in Florida.
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Chris (SilverUnicorn) wrote:

The first thing I would suggest is to add low vents to the soffets and maybe low in the end walls, near where the roof meets the bottom of the attic. This will produce way better flow of air up through the attic, cooling it and the house significantly.
I bought a "gable fan" at a thrift shop. Something like: http://www.nextag.com/BROAN-353-NA-Gable-617374296/prices-html My fan is more powerful than a standard window fan of similar size.
I put it in the opening to the attic, with an X10 remote control module on its power to control it. It functions as a small whole house fan, sucking air up from the house through the attic. This could be an easy thing to do which doesn't coast so much. I just slipped chunks of pipe insulation over the four mounting arms, and set it over the attic access hole, with the pipe insulation on the wood to isolated vibration and noise from the house structure. Open appropriate windows to produce airflow through the house, from the farthest windows to the fan.
You may need to bypass the built in thermostat in the fan so it will operate at lower temps.
The fan needs to be small enough to fit in the attic access door, and large enough to fill most of the hole. Baffles could be added to decrease backflow from the attic.
Here in Seattle, I run the fan at night, cooling the house off, then turn it off in the morning, closing the windows and curtains. The house will still be 5-9 F cooler than outside by the evening.
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In my first house I cut holes in my roof and installed two wind turbines. There was a very noticeable difference in the comfort level of the house when I came home from work in the summer. I then installed a whole-house fan but needed to add another vent to exhaust the attic air because the total square footage of the existing vents was less than the area of the fan. I added this vent so it exhausted into the garage which, after the attic had cooled, helped to ventilate the garage. The attic fans usually have a louvered shutter that opens automatically when the fan is on, either by the force of the fan or with a motor. This was a one-story, 1350 sq/ft house with poor insulation and the attic fan was a great improvement.
My second house was a two-story, also poorly insulated. I installed an attic fan and it seemed to help somewhat, but not as well as the first house. I got better cooling results at night by putting a 20" box fan in the window blowing inwards.
Now I have a new manufactured home with no attic but it is very well insulated and 20" box fans in the window are about my only choice and they work quite well as long as it's below 70 outside. On cooler nights I only need to use a 120mm 12 volt cooling fan.
Judging from my experience just about any way that you decide to remove the hot air from the attic is going to help, especially if someone is going to be using air conditioning. With wind turbines or an attic fan you would not be pulling air through the house, only the attic so air conditioning could be operated at the same time. With an attic fan it's more like one or the other.
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Chris (SilverUnicorn) wrote:

Hi, Where are you located? Having ridge vent, you need extra ventilation? First you have to find out whether you need extra vent. or not. Also what is R value of your atic insulation?(how thick?)
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Thank you for the replies.
We live outside of Philadelphia, PA. The house does have dual zone centeral air. The ridge vents are the only ventilation. Wait....I think we have soffit vents as well. Sorry, I don't know all the terminology. There are grated panels every so often under the edges of the roof. I think these are soffit vents?
This stuff:
http://www.wood-whitacreroofing.com/images/100_0262.JPG
That we have as well. Sorry for the lack of information.
Chris
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Chris (SilverUnicorn) wrote:

Yes, those are soffit vents. The attic vents - be they ridge or otherwise - are meant to allow hot air to escape. The air escaping draws fresh air in via the soffits. This continuous convection cools the attic. Not chilly cool, just cooler than if there were no convection.
--

dadiOH
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Chris (SilverUnicorn) wrote:

Most experts recommend 1 sq in of unobstructed soffit vent for each 1 sq ft of attic space. Assuming you have 1200 sq ft of attic space in a 2-story, 2400 sq ft home, you need 1200 sq in of soffit vents. That's an unobstructed vent totalling 1x8 feet.
The picture of venting material you provided is 98%+ obstructed. I'd say you need 400 linear feet of that stuff to reach the suggested level.
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We live outside of Philadelphia, PA. The house does have dual zone centeral air. The ridge vents are the only ventilation. Wait....I think we have soffit vents as well. Sorry, I don't know all the terminology. There are grated panels every so often under the edges of the roof. I think these are soffit vents?
This stuff:
http://www.wood-whitacreroofing.com/images/100_0262.JPG
That we have as well. Sorry for the lack of information.
Chris
*****************************************************************************
They are indeed soffit vents, and while they help, they are not enough to vent a whole house fan. You need gable vents at the ends too.
Getting back to the original question. A whole house fan will cool the house down if the outside air is cooler than the inside air. It will not remove humidity though, and the Philly area can be muggy. In the highest heat of the day, it will just suck in the outside hot air, but it will cool down the attic too. I rarely turn min on until evening when the outside temperature drops below 70. If the night is not going below 70, chances are AC is the better choice.
One night last week it was starting to get a little warm in the bedroom. I got up about 3 Am to go to the bathroom. I turned the whole house fan on and by the time I went back to bed, it sucked enough cool air into the house I got under a light blanket. Of course, a window fan could have done well also.
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On Tue, 21 Jul 2009 04:35:15 -0700 (PDT), "Chris (SilverUnicorn)"

If your primary aim is to cool the house then you want a whole house fan. An attic fan will pull much of it's air from the vents in the attic, which helps cool the attic, but doesn't do as much for the house. Whole house fans with automatic, tight sealing insulated doors are available, and they are very quiet and energy efficient, especially compared to older versions.
See for example: http://www.airscapefans.com/?gclid=CJ2U6LOV6JsCFZJM5QodG3cP5w
(A bit pricey, though, I might add)
You have to open a couple of windows when you run it, and you need enough vent area in the attic to exhaust the air, but otherwise they are fairly easy to install and use. The site above has good info on vent area needed, installation, etc.
Note that there are some disadvantages:
First, compared to air conditioning, you will be pulling more dust and dirt into the house.
Second, if you are using the WWF at night and in the morning, and then turning on the air conditioning during the hot part of the day, and you are in an area where it is very humid, you may not save very much over just running the a/c all the time. This is because it takes more energy to cool and dehumidify the air when it starts out with lots of humidity. The a/c cools and dehumidfies the air, then you run the WWF and pull a bunch of humidity into the house at night, then the a/c has to remove that the next day, and so on.... There are WWF sites out there that have charts that show (probably somewhat overblown) what sort of energy savings you can anticipate in various regions of the country.
HTH,
Paul F.
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wrote:

Generally "whole house fan" refers to a fan mounted in the ceiling of the top floor; it sucks air out of the house and blows it into the attic. For this to be effective, the attic must be well-ventilated; i.e. there must be lots of ways air can then get from the attic to outside. Adequate venting for a whole house fan requires a little bit of calculation: generally you need a vent area equal to the area of the fan. But for a vent with screen over it (which they all have), you have to reduce the area by some percentage (because the screen restricts the flow somewhat) to get the "effective area." So if installing a whole house fan, you would need to add up all the attic vents and calculate their effective area, to see if you have enough venting to match the area of the fan you want to install. If not add venting. A competent contractor should be able to do all that. I just followed the instructions that came with my fan. When the fan operates, it sucks outside air into the house (must have windows open), so it is ventilating the house, and is also ventilating the attic since the house air gets blown into the attic and then from the attic outside.
I installed whole-house fans in both houses I have owned; I like them. My climate is fairly similar to yours, at least in summer - variably hot and humid. As long as it cools off at night, I find the fan a nice alternative to AC. But as others have mentioned, you won't necessarily save a lot of energy. And some nights it will just not cool off enough to make it comfortable. Also I will say using a whole house fan requires a little bit of operational savvy; you get a nice breeze wherever you open a window, but you may have to prop the door open in that room so it doesn't slam shut. It's not rocket science but not completely foolproof. Whole house fans usually come with a timer switch so you can set it to run for, say, three hours, then shut off (good when you're going to bed and don't want it to run all night).
An "attic fan" or "attic ventilation fan" is mounted in the attic (in a gable or the roof) and sucks air out of the attic and blows it outside. Again, the attic must be well vented for it to work right; if there is not enough venting, some might have to be added. Attic fans are usually smaller than whole house fans and move less air. Their purpose is to ventilate the attic so it is not 140 degrees up there; that puts less heat load on the house and also helps prolong the life of your shingles. (A whole house fan also ventilates the attic.) As some folks have mentioned, when the attic fan is running you could also open up your attic access door and then it would suck air out of the house, like a whole house fan (but probably weaker). Attic fans usually have a temperature sensor that turns the fan on automatically when the attic temperature reaches a certain level.
It seems to me there have been some posts to this group about people having trouble with their attic-ventilation fans, that they stop working and/or catch fire! Not sure whether that is a real issue or just a fluke; you might try asking your insurance agent if they have any statistics on that.
From your picture it looks like some parts of the house have little or no attic space; those rooms might be unaffected by reducing the attic temperature.
Also as a longer-term measure, you might consider planting some trees in the yard to someday shade the house.
Cheers, -- H
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Solution: magnetic door stops. You open the door fully and a magnet in the door stop keeps the door from moving.
They may be hard to find and/or expensive but are well worth the effort.
I first saw them in several homes in China and thought they were bloody terrific. They're easily available and extremely cheap there so I brought a bunch home. I just love these little suckers; best thing since sliced bread!
--
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:>Also I will say using a :>whole house fan requires a little bit of operational savvy; you get a :>nice breeze wherever you open a window, but you may have to prop the :>door open in that room so it doesn't slam shut.
: Solution: magnetic door stops. You open the door fully and a : magnet in the door stop keeps the door from moving.
: They may be hard to find and/or expensive but are well : worth the effort.
: I first saw them in several homes in China and thought : they were bloody terrific. They're easily available and : extremely cheap there so I brought a bunch home. I just : love these little suckers; best thing since sliced bread!
They're available from Lee Valley.
    -- Andy Barss
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