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Whole house fan – ducting it outside instead of pulling air into attic

pitchblack | Posted in General Questions on

I want to get a whole house fan for shoulder season cooling efficiency and fresh air. I prefer a roof mounted unit for direct exhaust outdoors, but the only model on the market requires 24 inch center roof beam spacing, and I have 16 inch.

The reason I want direct exhaust is that I want to avoid attic air coming into the living space through either 1) not enough venting causing attic pressurization (and air coming out through outlets or other openings) or 2) escape through soffit vents as exhaust into open windows just below. Basically, I don’t want nasty attic air coming into the home.

The solutions I have seen besides a roof mount include:
– Mounting the whole house fan in the attic and ducting outside through the roof
– Mounting the whole house fan in front of a large gable vent
– Covering the soffit vents during the spring through fall and installing lots of ridge venting
– installing multiple attic fans to pull the air out of the attic through the roof

The first I’ve heard as an option but never seen it done or explained. The second I’m not positive will work on its own without lots more venting. The third seems too labor intensive. The fourth is reliant on attic fans which are prone to break down or short out.

Any ideas or thoughts? If this doesn’t work out we may go for another solution for fresh air. I realize whole house fans don’t work when it’s humid out but we still like the idea and want to make it work if possible

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Replies

  1. Expert Member
    Michael Maines | | #1

    Here are a couple of good articles that include powered attic venting:

    https://www.greenbuildingadvisor.com/article/fans-in-the-attic-do-they-help-or-do-they-hurt

    https://www.greenbuildingadvisor.com/article/all-about-attic-venting

    Generally speaking, in most cases, they hurt more than they help. It's usually better to air-seal the connection between attic and living space and add more insulation to the attic floor.

    1. pitchblack | | #2

      Even with proper sealing (which may prevent air coming out fixtures and sockets), soffit venting could still potentially lead to attic air coming inside.

      I wonder though about the physics of venting. If adequate ridge venting exists (I'm talking about 30+ feet plus a power vent), should soffit venting be minimal? Since I'd expect the hot air to want to rise out of ridge vents instead of down through soffits and into the living space.

      1. Expert Member
        Michael Maines | | #8

        If you oversize the ridge vent compared to the soffit vents, or don't use soffit vents at all, or you use a powered vent, unless your ceiling air barrier is perfect, you will draw air from inside the home.

  2. Expert Member
    DCcontrarian | | #3

    An option I don't see is not involving the attic at all -- just having the fan in the living space somewhere and venting directly outside.

    I love whole house fans, but the challenge is how to seal them when they're not in use.

    1. pitchblack | | #4

      I actually have an AirKing window mounted whole house fan but it's too tall (26'') for my window, making mounting difficult. But this would require opening the window, removing the screen, mounting it, and screwing it in every time I want to use it, then removal afterwards (otherwise bugs would get in).

      I guess there are also whole house fans that you can build into a wall, is that right ? Are there quality product options available in that vein?

      1. Expert Member
        DCcontrarian | | #7

        There isn't an out of the box solution that does what you want, it's going to require some construction.

  3. walta100 | | #5

    The one on my last house was great about 15 days a year but it was so noisy the wife would not tolerate it even when it was ideal conditions. The rest of the year it was a leaky uninsulated hole in the ceiling I think is lost way more energy than it ever saved.

    Consider ducting it to a set of louvers on the gable end wall.

    Walta

    1. pitchblack | | #6

      Automatic louvers that shut when the fan isn't in use? Yea there would have to be more than one to meet the square footage of venting required.

      Can you help me visualize what you're thinking of? This may be what I'm looking for.

  4. walta100 | | #9

    Much like the install shown on this website but with a duct in the attic so all the air comes up from the ceiling.

    https://www.protoolreviews.com/how-to-install-commercial-wall-exhaust-fan/

    1. pitchblack | | #10

      Very nice ! Thank you !

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