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Community and Q&A

Attic fans

tds968 | Posted in General Questions on

I live on Long Island in NY state close to the ocean and have two fans in my attic — they have been there since I bought the house and I have already replaced them once BUT after reading your 10/12 article re these fans, I’m wondering if I should disconnect them. My attic floor is insulated with blown in cellulose and I have soffit vents and four normal passive vents already in the roof. I do have my air-handler in the attic along with soft duct work to various top floor A/C outlets. My home is 73′ x 31′

It makes sense to me that these fans are drawing my air conditioned cool air into the attic but I was concerned that I could cause damage to something if I disconnected?

Thanks for any help you can give me.

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  1. GBA Editor
    Martin Holladay | | #1

    If the article you read is this one -- Fans in the Attic: Do They Help or Do They Hurt? -- then I can't imagine that my words were hard to understand.

    I wrote, "At the risk of oversimplifying, whole-house fans are good. Powered attic ventilators are bad. ... Powered attic ventilators ... can cause a host of problems. ... In many homes, powered attic ventilators pull conditioned air out of the home and into the attic through ceiling cracks. The net result: powered attic ventilators increase rather than decrease cooling costs."

    If the fans in your attic are powered attic ventilators -- and it sounds like they are -- you should unplug them or (safely) cut their cords.

  2. tds968 | | #2

    Sorry if you think I didn't understand your very clear article --- my mistake, since I did not mention that my roof is a "hip" roof and I heard that could make a difference since ridge ventilation may not function with a hip roof. I'm thinking that my four passive vents along with the natural vents created by two non-working attic fans may be enough?

  3. Expert Member
    Dana Dorsett | | #3

    Attic ventilation is about purging moisture, not heat.

    Most of the heat gain of the ducts & air handler in the attic are from heat radiated from the roof deck, not the attic air. The roof deck temperature responds far more quickly to solar intensity than it does to ventilation, and the amount of ventilation power it would take to make an appreciable difference typically exceeds the amount of air-conditioning power use it's offsetting.

    And if the fans depressurize the attic it pulls air from both leaking ducts and air leaks in the attic-floor plane of the house, cooling the attic by parasitic leakage from conditioned space. When you have ducts & air handlers in the attic (a universally bad, if common practice) the most important thing for maintaining efficiency is to air seal the ducts, and air seal all penetrations of the attic floor, followed by insulating the ducts.

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