Size of whole house fan needed
Does any one have an hour of free time to help me figure some thing out.It probley will not even take that long.
I got a whole house fan from lowes and it does not seem big enough
I was not to sure on how to figure out the the size fan needed for our
size house.I read on line to take the square footage of the house and multiply that by 3 and that would tell you the cfm you need to cool
the house properly.
I was not sure if I read that right so I called the manurfacture of this
fan and they said this fan would work fine so I got it and installed it and it does not seem very good at all.
So before I go and try to return this I wanted to see if someone could
take the mesurements of our house which is 1350 sq ft and the size of the fan which is 2200 CFM and see what you come up with.
I know that the attic has to have proper ventalation for the air to
escape we have vents in the eaves and two gable vents and a whirly
I am not positive that those vents are all that needs to be in the attic for proper ventalation but I know its pretty close.
You can even get the specs of the fan just do a search it is a
If taking the square footage and multiply by 3 is a correct way to figure out the size of fan needed then I think I will be pretty pissed at the manurfacture of that fan.
I am pretty sure that the fan is way to small but I am trying to avoid having to return this fan and then having a hole is the ceiling to deal with.
So I want to make sure forsure that this fan is not good for this size house before I remove it.
Thanks for any help you can give me. Doug
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
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
Dam it seems like every thing I do I run into problems.
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?
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.
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.
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
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.
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.
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.
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?
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.
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:
But then again I am not an expert. :huh:
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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