Attic fan with open attic window?


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Old 08-21-14, 11:26 AM
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Attic fan with open attic window?

I have an attic vent fan as well as an attic window. I was wondering if I should keep the attic window open in the summer while the vent fan is in use?
 
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Old 08-21-14, 11:38 AM
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I say keep the window closed to prevent rain and birds from getting into the attic. A hard blowing rain could let a lot of water in. Do you have soffit or gable vents for air to enter the attic?
 
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Old 08-21-14, 11:47 AM
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To prevent a negative pressure in the attic space, which would draw conditioned air from your living space, your attic will need an opening that will allow in at least the cfm amount of air that's being discharged by the fan.
 
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Old 08-21-14, 02:08 PM
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The window is screened and covered so no rain or animals can get in. I have soffit and ridge vents. I was wondering if closing the window would force air to come through the soffit vent and discharge hot air better. Or is leaving the window open a better way to discharge hot air. Note that I have lots of stuff in my attic, non of which are on top of the soffit vents but may be blocking air flow. I'm not moving any stuff. Thanks for the info...
 
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Old 08-21-14, 04:26 PM
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The airflow will take the path of least resistance. So, an open window could allow most of the air to be drawn through it and less to flow through your soffit vents.
 
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Old 08-21-14, 05:20 PM
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thanks for the reply. The question is what is better. air flow through the window or soffit vents?
 
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Old 08-21-14, 05:39 PM
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It really isn't going to matter where the air comes from, unless of course if the fan is next to the window. The more the attic can breath, the better it will be. Where's the fan located?
 
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Old 08-21-14, 05:42 PM
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Actually, leaving the window open will increase the flow through the soffits, with and without the fan running. Allowing more air out will shift the neutral pressure plane upwards increasing the pressure difference across the soffits, thus more air coming in.

The real concern is operating the vent fan will require as much intake area as possible to minimize the negative pressure as SeniorCitizen mentioned. As long as rain (or snow) is not an issue, be sure to consider the wind as well, then leaving the window open is best for ventilation. It may also reduce the run time needed for the fan.

Bud
 
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Old 08-21-14, 06:09 PM
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Thanks that's what I was wondering. I'll keep it open for the summer. I shut the window when it gets cool out and the fan doesn't run any longer.
 
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Old 08-22-14, 05:11 AM
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Id close the window and cut the fan off because you have ridge and sotfit vents. The fan will short cycle the air.
 
 

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