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  1. #1
    Join Date
    Apr 2012
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    212

    Question Measuring Attic Space For Fan

    I have a small attic above my 2 1/2 car garage. It gets very hot up there sometimes and I wanted to add either a small solar fan, or a whirlybird turbine ventilator (shown below) but I don't know the math formula to figure out what size fan to use. Because the roof comes to a point, how do I future in the height?

    Also, how well do these whirlybird turbine ventilators work? I've seen them before but can't imagine they remove much heat. Can anyone explain how they work? Thanks.



  2. #2
    Join Date
    Aug 2007
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    7,243

    Default Re: Measuring Attic Space For Fan

    To find the volume of a pyramid, multiply the area of the base X height X 1/3.

    Can't answer the question about Whirlybirds, the main thing is that you want good convective airflow (cool in from the bottom, hot exhausts out the top ). You will need to add venting at the soffit or base of the walls, if you don't have that already if you want to see benefit from a roof vent. A more attractive option would be to install an eyebrow vent.
    I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!

  3. #3
    Join Date
    Apr 2012
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    212

    Unhappy Re: Measuring Attic Space For Fan

    Quote Originally Posted by A. Spruce View Post
    To find the volume of a pyramid, multiply the area of the base X height X 1/3.
    Thank you

    You will need to add venting at the soffit or base of the walls, if you don't have that already
    Yes it has venting all around the sides.

    A more attractive option would be to install an eyebrow vent.
    It already has two small (10"?) vents like this. They don't seem to do very much.

  4. #4
    Join Date
    Aug 2007
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    7,243

    Default Re: Measuring Attic Space For Fan

    Here is something that might help understand how a Whirlybird works.
    http://www.solarsucker.com.au/whirlybird/

    IMHO, they're not very attractive, and not likely too efficient, unless you've got regular decent winds. I'd go with a power vent option, a thermostatically controlled fan. Most of these are gable fans, though I've seen a few mounted into an eyebrow vent. I suspect you could rig up something similar with the eyebrow vents you already have, you'd just have to come up with a small fan to fit the housing, then a means of mounting. Electrical is as easy as providing an outlet to the location, and you can either manually switch it in the garage, install a timer switch, or a thermostatic switch.
    I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!

  5. #5
    Join Date
    Apr 2012
    Posts
    212

    Lightbulb Re: Measuring Attic Space For Fan

    Quote Originally Posted by A. Spruce View Post
    I suspect you could rig up something similar with the eyebrow vents you already have, you'd just have to come up with a small fan to fit the housing, then a means of mounting.
    I was reading that one solar fan equals around 15 Whirlybird fans, so I doubt I will get a Whirlybird now. Unfortunately the solar fans are so over priced. Cheapest I've found was around 225.00. According to the calculations on the Broan fan calculator HERE I need to move around 368 CFM. This means that most of the solar attic fans are overkill, because they push over 1100 CFM. If I could find a generic solar fan I'd be able to mount it under the vents that I have now. I'm thinking about mounting 4 computer fans together, and solar powering them.

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