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Re: Attic ventilation from fans

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On May 16, 2006, at 7:54 AM, Paul Ransom wrote:

Manufacturer's data? website?
Canada has an exceptionally good residential energy code that Minnesota has used to help with our, which is also pretty good, judging from the amount of whining and bitching from the construction business about it. Google around for attic ventilation references in local energy codes.

I have these on my house installed by the previous owner. The throat
size of the vent is limiting and the momentum of air passing through
must also give up energy to spin the turbine. I do not believe that they
provide additional ventilation but they look like they are doing
something. Gives buyers a level of comfort to see activity.
I suspect the real limiting features are the small area between blades and the fact that you need wind to turn the damn things. Unless they're kept well lubricated they aren't going to turn fast enough to overcome the velocity pressure of the wind on the upstream side or pump interior air through the leeward side. When you think about it, it seems like a violation of the Second Law: like a wind powered window fan. It can't possibly be as effective as an unblocked open window.

Christopher Wright P.E. |"They couldn't hit an elephant at
chrisw(--nospam--at)   | this distance" (last words of Gen.
.......................................| John Sedgwick, Spotsylvania 1864)

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