# Size of whole house fan needed



## redline (Mar 5, 2006)

It appears that the fan is too small. See link below

This was a clearance fan because it is noiser than other models. see link below


http://www.eere.energy.gov/buildings/info/homes/wholehousefan.html

http://www.energyfederation.org/consumer/default.php/cPath/421_1364


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## Doug Crf (Apr 5, 2006)

redline said:


> It appears that the fan is too small. See link below
> 
> This was a clearance fan because it is noiser than other models. see link below
> 
> ...


Hi redline hay I seen you said it appears that the fan I have is to small.
I am wondering if you say that because you did the math.
That stuff is to confusing for me to try to figure out.
The fan I have is that exact one on the energyfederation site you mentioned there.
I am thinking it would be pretty hard to mesure the attic space and probley to confusing for me.
I am wondering if this would be a good idea,What do you think?
Run the fan and go out to the gable vents and see if I feel any air comming out and how much.
If I barley feel any then I know for sure that there is not a venting problem.
If there is alot of air then it could be a venting problem.
Or should I find and hire someone to come do the mesurements 
for me.
Dam it seems like every thing I do I run into problems.
Thanks Doug


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## redline (Mar 5, 2006)

This is from the DOE web site.

_______________________

"Sizing A Whole House Fan
Determining the amount of airflow in cubic feet per minute (cfm) that the whole house fan should provide involves a simple calculation. Multiply the total gross square footage of the house (include upstairs area) by the ceiling height (typically 8 feet). Select a fan that delivers between one half to one times that amount of cfm at 0.1" static pressure. For example, a 25'x40', one-story home is 1,000 square feet and would need an 8 x 1,000 x 0.5 = 4,000 cfm fan or better. A manufacturer sells a two-speed unit that delivers 4,500 cfm at the high setting (240 watts) and 3,200 cfm at low (120 watts); this unit should be adequate. "


___________________________________

The example above states that a 1,000 square foot house needs a 4,000 cfm fan or better. Your house is 1350 (larger than 1,000) which means that you need a fan even higher than the 4,000 cfm in the example. I believe that yours is only 2200 cfm.

What is the outside high temp in your area?


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## Doug Crf (Apr 5, 2006)

Hi Redline 
When I first started checking out these fans I had read on a site how to do the calculation to see what size fan I would need and I think I came up with close to the same cfm needed as you said I would need.
So I got to thinking if my calculations were right then the 2200 cfm that I have would only be good for a house like 600 of 700 sq feet or
some where around that size.
Since there are not to many houses that size I figured I might not be doing the calculations right so I figured I would call the manurfacture and see what they thought and when they said the fan would be good.I thought well I must of did the calculations wrong.
So I went and got the fan.
I sent an e mail to this other company acting like I want to buy a fan
from them and I ask them what fan of theres I would want to get with the size of our house and they said they have this one that is rated at 1000 cfm model hv-1000 and they said that one would work good.
They also have another one the same deminsion's that is rated at 1600 cfm and they did not mention that one.
I am lost.
Yesterday I went up and checked out the cable vents and they were pretty pluged up with junk and paint so I cleaned them and there is a pretty good amount of air comming out of them.
Below one of the vents there is a tree like four feet away and I can see the leaves blowing a little when I have the fan on.
So I guess either I need to mesure the vents and see if I have enough vents or I am just thinking I am going to go ahead and have a couple more vents installed on the roof.I would think the more venting the better.
I just do not want to take this fan down and take it back to lowes if it is the right fan and I am the one making the mistake.
Thanks Doug


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## Bob Anderson (Mar 21, 2008)

*Whole House Fans - My 2 Cents*

We bought a Tamarack whole fan 2 or 3 years ago and it works great. They key to it is to only turn on once the outside temp is lower than inside. Also, the insulated doors keep out the cold and hot when not in use. We also use a timer to run the fan until 6 or 7 am and then it turns off as the outside temp goes on. Also, last year I bot a solar attic fan to help when the whole house fan is not in use. It seems to work as expected - but we need another summer to know for show. 

Bob


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## mtcone (May 19, 2008)

Square feet of vent needed = Volume of Home / 750 (volume = sum of all rooms LxWxH) 
Total Air Volume of House / 3 = Ideal CFM (cubic feet per minute) of Fan 

Hope this helps. 
Here is a link that might be useful: Whole House Fans


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## [email protected] (Jun 22, 2008)

Doug,

I'll go along with what Bob Anderson posted. I lived in a shotgun style house for 30 years. We would turn the fan off before the outside air got as warm as the inside air. People tend to forget to turn off the fan or are not aware that the temperature outside is the same as the inside temperature because the breeze feels good if the temperatures are equivalent. I had an upstairs floor in the camelback shotgun house, so the temperature upstairs was much higher than the temperature downstairs. I based my decision to turn off the fan on the downstairs temperature verses the outside temperature, and ignore the upstairs temperature.


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## Robertb (Feb 22, 2011)

*Whole House Fan Calculator*

I found an on line calculator that figures out how many cfms any particular whole house fan will put out based on the square footage of my house. Here it is. http://www.ilocano.net/suburbanFan/

I made a mistake and purchased my whole house fan from an on line supplier in CA ( where I live ) and had to pay tax on the sale..Ouch! 

The fan works great...Very quiet.


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## Ron6519 (Mar 28, 2007)

You don't vent a whole house fan out of holes in the attic. You install a dedicated shutter vent in the gable wall.
Whole house fans work better if the fan is mounted in the gable to blow directly outside. There should be a shutter vent in the main hall ceiling that will open when the fan is turned on. The suction of the fan will open the shutter. It will close when the fan is turned off.
Ron


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## mitchel (Aug 4, 2008)

Ron6519 said:


> You don't vent a whole house fan out of holes in the attic. You install a dedicated shutter vent in the gable wall.
> Ron


I'm not an expert, but that makes no sense at all. How is this going to blow out the hot air that is acumulated in the attic?

Everything I read says that the fan is supposed to suck in cooler air from the outside and at the same time force the air that is in the living space and attic out of the house to help cool things off. What sense would it make to keep the super heated air in the attic?


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## Ron6519 (Mar 28, 2007)

mitchel said:


> I'm not an expert, but that makes no sense at all. How is this going to blow out the hot air that is acumulated in the attic?
> 
> Everything I read says that the fan is supposed to suck in cooler air from the outside and at the same time force the air that is in the living space and attic out of the house to help cool things off. What sense would it make to keep the super heated air in the attic?


There are attic fans and whole house fans. They are used in different ways. An attic fan is used to remove superheated air from the attic, and only the attic. It can be mounted on the roof, near the ridge or it can be gable mounted. It works better with soffit vents as it will draw relatively cooler air from the exterior, up the roof line and out of the house. It has a thermostat that you set so it goes on automatically.
A whole house fan is meant primarily to cool the house. It can be mounted in the ceiling that goes into the attic or it can be mounted in the gable wall. In either case it requires 2 shutter vents. One at the fan and one on the gable exhaust site. If you mount the fan in the ceiling without a shutter vent you will create a back pressure and the fan will not move the amount of air it's capable of. As a result you will think it's too small for the house.
I like to mount the fan on the gable as it eliminates all the back pressure. and exhausts directly to the exterior. As it does, it pulls the air in from the open windows and doors of the house, through the ceiling shutter, creating a breeze. If there aren't enough doors and windows open, the fan will not operate properly and you will think the fan is too small for the house. It will also suck air down the chimney pulling carbon monoxide into the house if the hotwater heater or the boiler are running.
It has the added benefit of removing the superheated air from the attic, but only when it's on. 
So while your fan may be too small, it's more likely it's either installed incorrectly or being used incorrectly, or both.
Ron


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## mitchel (Aug 4, 2008)

Sorry, but this still goes against everything I have ever read about a whole house fan.

Take a look at this site, this is the way it was explained to me:

http://www.wholehousefan.com/HOW-IT-WORKS/Ceiling-Mounted.html

But then again I am not an expert. :huh:


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## Ron6519 (Mar 28, 2007)

mitchel said:


> Sorry, but this still goes against everything I have ever read about a whole house fan.
> 
> Take a look at this site, this is the way it was explained to me:
> 
> ...


Then you should do it the way you're comfortable with. 
Ron


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## High Gear (Nov 30, 2009)

One of the problems with a whole house fan is many times the amount of 

ventilation needed to run properly is more than you should normally have.

If you don't have enough venting then the air velocity can cause your vent 

screens to plug with insulation.

Ron's method I believe is to duct it from the ceiling to the gable , I've not 

seen it done this way but it makes perfect sense.


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## Ron6519 (Mar 28, 2007)

High Gear said:


> One of the problems with a whole house fan is many times the amount of
> 
> ventilation needed to run properly is more than you should normally have.
> 
> ...


You can duct it, but I never saw the need. Plus being unducted, it clears the attic of heat.
And as High Gear said, attic ventilation is inadequate for the fan. As a matter of years of observation in many, many attics, they are not adequately vented for a static elimination of hot air, much less a dynamic source pushing 1600+ cfm's a minute. You end up pushing that air back into the house. You'll feel the air coming through the outlet and switch boxes.
So unless you've set the house's venting to accomodate the new load, it will be like the fan is undersized and won't work properly.
Ron


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## FixitDragon (Feb 9, 2011)

A few years ago we bought a whole house fan, I think it is a Tamarack, we bought it as a closeout at home depot (first clue). It has the twin 12" direct drive fans (second clue) and a insulated door that opens and shuts. It does not work well. It does not move enough air for our 1200ft home. The attic has 2 12" whirly turbin vents, and 2 large (15x30) gable vents, so venting isn't the problem. Biggest problem is the noise. It is SO LOUD (Think B-17). It is mounted in the hallway, and we can't watch TV in the living room, and can't leave it on after anyone goes to bed. So it doesn't get used which is a real shame. Where we live the evening temperature is almost always cool, but because of where our house is and the way it is positioned, we get ZERO natural airflow through windows and doors. I am this spring going to move it into the attic and try ducting it to see if it quiets and improves flow. I may just have to try something else.


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## Ron6519 (Mar 28, 2007)

FixitDragon said:


> A few years ago we bought a whole house fan, I think it is a Tamarack, we bought it as a closeout at home depot (first clue). It has the twin 12" direct drive fans (second clue) and a insulated door that opens and shuts. It does not work well. It does not move enough air for our 1200ft home. The attic has 2 12" whirly turbin vents, and 2 large (15x30) gable vents, so venting isn't the problem. Biggest problem is the noise. It is SO LOUD (Think B-17). It is mounted in the hallway, and we can't watch TV in the living room, and can't leave it on after anyone goes to bed. So it doesn't get used which is a real shame. Where we live the evening temperature is almost always cool, but because of where our house is and the way it is positioned, we get ZERO natural airflow through windows and doors. I am this spring going to move it into the attic and try ducting it to see if it quiets and improves flow. I may just have to try something else.


 They have gable mounted fans that move up to 9000 cfm's. Ventamatic is one company that sells them. You leave a shutter in the ceiling and mount the fan in an attic wall. You can put rubber dampeners against the studs to minimize vibration and resonance.
Ron


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## High Gear (Nov 30, 2009)

Out of curiosity Ron , are you relying on the suction from the fan to open the 

ceiling vent or are you using a shutter motor.

Being that your drawing from all the vents I think you would have to use a 

shutter motor.


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## Ron6519 (Mar 28, 2007)

High Gear said:


> Out of curiosity Ron , are you relying on the suction from the fan to open the
> 
> ceiling vent or are you using a shutter motor.
> 
> ...


I've never needed a shutter fan motor. These fans have an incredible pull to them and all houses are under vented. The shutters pop open before the fan reachs full power. 
The same is true if you mount the fan in the ceiling and put a shutter on the gable wall. It blows open in a heartbeat.
Ron


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## High Gear (Nov 30, 2009)

I installed this fan yrs ago in a previous home and can attest to there draw.

Brick gables with small vents and a shallow attic steered me to a ridge vent 

and deflectors because of cellulose dust and the velocity in the small space.

Mounting on a gable would certainly cut the noise level vs ceiling mount,....interesting .

Thanks for the info , don't know if I'll put one in here yet but I like your 

method.



http://www.grainger.com/Grainger/DAYTON-Whole-House-Fan-5NRT2?Pid=search


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