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Thread: turbine vents

  1. #1
    RobertSmith's Avatar
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    Default turbine vents

    Last edited by RobertSmith; 12-20-2007 at 08:52 AM.

  2. #2
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    Default Re: turbine vents

    Not for the conditions in your picture. I heard quite some time ago that these things really don't work that well but I can't remember the dynamics of the reasoning. I tend to wonder if they have the same trouble as ridge vents without baffles.

    Eric Barker, ACI
    Lake Barrington, IL

  3. #3
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    Default Re: turbine vents

    Robert,

    I always give the turbines a spin to make sure they rotate freely. Sometimes the bearings become rusted so that the turbine won't spin and then its a source for water entry.

    As Eric mentioned turbines don't always work well on some homes. Most people think they work by being wind driven but I think they work best by the heat in the attic rising causing them to spin.

    If your ever standing next to one during the summer months, you can definately feel the heat coming from the attic.

    Funny story, years ago I was dusting a attic with a power duster for carpenter ants. This machine can blow out a pound of dust in just a few seconds creating a cloud that covers the attic. I came down from the attic door and walked to my truck to put the machine in the tool box. I turned around and it looked as if the house was on fire or something. That dust was just pouring out of the turbines like it was smoke. The lady next door came outside and wanted to know if she needed to call the fire dept. Lesson learned there for me. Cover the turbines first before dusting.

    rick


  4. #4
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    Default Re: turbine vents

    A turbine vent only works when the wind is blowing. If the wind is not turning it, then it is just getting in the way.

    The arguments against them are:

    1. They only work when the wind is blowing, and conventional vents work fine under those conditions.
    2. They can be noisy.
    3. If it is really windy and there is not enough soffit venting, they can depressurize the attic space and pull air and moisture from inside the house. This is bad in a cold climate.

    I recommend against them in a cold climate.


  5. #5
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    Default Re: turbine vents

    Rick has it right, rising heated air causes spin enhancing heat withdrawal from attic spaces. Wind in not a factor and they are an excellent venting system as long as they are maintained in good working condition.

    Jerry McCarthy
    Building Code/ Construction Consultant

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    Default Re: turbine vents

    David, I disagree.

    A turbine vent only works when the wind is blowing. If the wind is not turning it, then it is just getting in the way.
    Turbines typically have a short stack which increases the convection movement (hot air rises) just like a taller chimney will improve the draft, whether the wind is blowing or not. Wind improves the performance, but wind is not a prerequisite for wind turbine function.

    I can't speak to the pros or cons about cold climates, but around here, I'll take any help we can get on hot attics.
    And yes, you need soffit vents in addition to turbines for proper performance.

    Jim Luttrall
    www.MrInspector.net
    Dallas, Texas

  7. #7
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    Default Re: turbine vents

    If you want stack effect, just extend the vent above the roof.

    Think about it. The kinetic energy from the rising air spins the turbine, therefore the air gives up some of its kinetic energy to spin the turbine. Less kinetic energy (velocity) - less air out the vent. To get more air out of the vent, the fan would need to add energy to the air moving through it, not take it away.

    For the vent to draw more air out of the attic than you would get with a simple hole, we need to add energy - either from the wind turning the turbine, or with an electric fan.


  8. #8
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    Default Re: turbine vents

    I got you David, except even a hole has to have a cover and I doubt the wide slot openings in the turbine as well as the gap between the stack and the spinning turbine would obstruct the opening much more (if any) than the flat cover of a standard flat vent.

    Then add the screen mesh in the standard flat vent which is not present on standard turbines and I think the energy argument is pretty much a wash.
    Then add the fact that the exiting air spins the turbine AFTER it has exited the stack and is past the lower gap, and you see it is the energy of the rising air in the atmosphere, not the pressure of air pushing out of the attic that spins the turbine, and therefore no energy lost to the spinning of the turbine.

    Jim Luttrall
    www.MrInspector.net
    Dallas, Texas

  9. #9
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    Default Re: turbine vents

    The only way you can not lose energy is if the fan is 100% efficient and the bearings have zero friction.

    However, you are correct that there are also losses in a normal roof vent that reduce its effective area. If all other things were equal, a conventional vent would move more air than a turbine if there was no wind.

    Also, since a conventional vent is essentially a hole in the roof, it can allow moisture into the attic. So it might be beneficial to have fewer vents (and holes) that get some help from the wind.

    In a warm, moist, windy, climate, I can see how a turbine vent would be a good thing.

    No simple answers. That's what makes this fun.


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    Default Re: turbine vents

    Quote Originally Posted by David Wood View Post
    A turbine vent only works when the wind is blowing.
    As others have stated, that is incorrect.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

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    Default Re: turbine vents

    Quote Originally Posted by Jerry Peck View Post
    As others have stated, that is incorrect.
    OK, I did not word that correctly.

    The fact that the vent turns when there is no wind is proof that there is air moving through the vent - so the vent does "work".

    However, my point is that the fact that the turbine is spinning does not necessarily mean that it is pulling air from the attic. Air moving through the vent due to convection can push the turbine - and give up some of its energy in the process.

    Another challenge of this work. Saying what you mean in a way that can not be interpreted in another way.


  12. #12
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    Default Re: turbine vents

    Quote Originally Posted by Rick Hurst View Post
    Sometimes the bearings become rusted so that the turbine won't spin and then its a source for water entry.
    Rick, it won't leak only if its spinning?


  13. #13
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    Default Re: turbine vents

    Quote Originally Posted by David Wood View Post
    Think about it. The kinetic energy from the rising air spins the turbine, therefore the air gives up some of its kinetic energy to spin the turbine. Less kinetic energy (velocity) - less air out the vent. To get more air out of the vent, the fan would need to add energy to the air moving through it, not take it away.

    For the vent to draw more air out of the attic than you would get with a simple hole, we need to add energy - either from the wind turning the turbine, or with an electric fan.
    I've been pondering this imponderable off and on and I fail to see where that would have even a negligible effect on the amount of air which is being exhausted from the attic.

    'Could' it be measured? Sure, with a manometer. Will it realistically effect the attic ventilation? I seriously doubt it.

    That's like saying that rain gets shingles wet, and, eventually, the moisture gets through the shingles. Yeah, they do and it will, if it never stopped raining - but it always does, and then things dry out. Thus there is no realistic effect on the shingles during a rain.

    'Could' is a laboratory theoretical aspect which does not affect real life installations.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

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    Default Re: turbine vents

    But it is being suggested by some that they can actually improve the air flow through the vent when there is no wind.

    At best they won't get in the way too much.


  15. #15
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    Default Re: turbine vents

    Air Vent - Mfg. says these vents need wind to operate properly.

    Air Vent: Wind Turbines


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    Default Re: turbine vents

    I've watched those turbine roof vents spin like Dervishes on hot windless days and given that the attic space was equipped with eve vents more hot air was sucked out of the attic area then a politician after losing an election. The only better method is thermo-controlled electric fans, which I installed my home. If I left the attic access door open on a hot day it cooled the entire house, sort of like a whole-house fan, but the cheapo version. The truth is that rain (wetness) doesn’t destroy roof coverings, heat does. Anyhow, that’s my take. Merry Christmas to all!

    Jerry McCarthy
    Building Code/ Construction Consultant

  17. #17
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    Default Re: turbine vents

    "these vents use the natural force of wind and air pressure to spin and vent out stale attic air."

    Jerry McCarthy
    Building Code/ Construction Consultant

  18. #18
    imported_John Smith's Avatar
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    Default Re: turbine vents

    GAFs website seems to indicate that wind is required for their units to operate efficiently. They specifically make their references to a wind velocity of 8 mph in calculating size and number of vents. If no wind was required for proper operation, I think they wouldnt even reference it.

    Although these things were widely used, everyone I speak with about them (and in the hot humid Houston climate, attic ventilation is a frequent discussion topic) seems to think they are garbage (me included).

    But then again when I think of things spinning due to hot air rising, I seem to recall some Christmas decoration my parents had that would spin with a candle under it.


  19. #19
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    Default Re: turbine vents

    Quote Originally Posted by imported_John Smith View Post
    GAFs website seems to indicate that wind is required for their units to operate efficiently.
    "efficiently"

    Those are "100% efficient" regardless. (Because you are using no input power to provide work, you may have a reduced air flow by some degree due to getting the turbine to spin, but, compared to 'no turbine installed and no hole' you have achieved the unachievable - 100% efficiency.) Now, to make the air move better, add a fan, but that adds a power use factor to compensate for.

    Wind turbines work with "NO WIND", however, 5 mph (some brands) and 8 mph (some brands) *is the wind speed their ratings are to*. Does not mean they 'do not work' without wind, just means that there is no rated cfm with no wind.

    *IF* you are installing them to meet a specific cfm requirement, you must use a rating, and that rating is 'with wind', and not just 'with wind', but with 'a specified wind speed'. They are more efficient 'with wind' - hmmm ... how can you get more efficient than 100% efficient?

    *IF* you are installing them to get better attic ventilation, you ignore any and all ratings anyway, you install 12" or 14" ones based on your budget.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  20. #20
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    Default Re: turbine vents

    Quote Originally Posted by jerry peck
    Those are "100% efficient" regardless. (Because you are using no input power to provide work, you may have a reduced air flow by some degree due to getting the turbine to spin, but, compared to 'no turbine installed and no hole' you have achieved the unachievable - 100% efficiency.) Now, to make the air move better, add a fan, but that adds a power use factor to compensate for.


    This is just WRONG = They are not 100% efficient - no mechanical equipment is 100% efficient.

    Efficiency = Energy out/Energy in X 100 – “Some air coming out” doesn’t make it 100% efficient. That’s a FACT of physics.

    Quote Originally Posted by Jerry Peck
    Wind turbines work with "NO WIND", however, 5 mph (some brands) and 8 mph (some brands) *is the wind speed their ratings are to*. Does not mean they 'do not work' without wind, just means that there is no rated cfm with no wind.
    .


    Another thing – WRONG. They don’t work with “NO WIND”. They require wind to work.

    If you go in an attic and see mold all over the plywood deck and there is a 6inch gable end vent, with no soffit vents – do you say it works cause air is leaking out a 6 inch vent? Do you say it’s 100% efficient because you are using no input power?

    It doesn’t work.

    In order for it to work it needs to meet specific criteria. The criteria for these turbine vents are defined by the manufacturer’s ratings and good design/installation practices for ventilating an attic.

    It they don't meet the criteria they don't work.


  21. #21
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    Default Re: turbine vents

    Quote Originally Posted by Ken Amelin View Post

    This is just WRONG = They are not 100% efficient - no mechanical equipment is 100% efficient.


    Guess you missed the in there:

    Quote Originally Posted by Jerry Peck View Post
    Those are "100% efficient" regardless.
    Another thing – WRONG. They don’t work with “NO WIND”. They require wind to work.


    That is where you are "just WRONG" ...

    They DO *work*. They just do not work 'as efficiently' as when there is wind.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

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