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Attic Fan: Can You Save Money on Air Conditioning Costs?

  • Transcript

    LESLIE: Scott in Alabama is calling in with a question about an attic fan. What’s going on?

    SCOTT: Well, I wanted to know the wisdom of putting in one; does it really make a difference on your utility bills and everything. And also, is it better to have one that’s electric or solar?

    TOM: Now why do you want to put in an attic fan, Scott? Is it because you have central air conditioning?

    SCOTT: Yes.

    TOM: And you’re looking to reduce attic temperatures to reduce those costs?

    SCOTT: Yes.

    TOM: Well, here’s a surprise for you. If you put in an attic fan, you may very well increase your central air conditioning cost. You know why?

    SCOTT: Why.

    TOM: Because those fans can be so strong that they depressurize the attic and then reach down deep into the living spaces of your house and pull out air conditioned air. They’ll find little gaps inside the walls, where wires run and things like that, and it’s been shown that using an attic fan can actually increase air conditioning costs. So an attic fan I think generally is a bad idea. You’re almost always better off using passive ventilation – like a ridge vent, a soffit vent, that sort of thing – to reduce attic temperatures and not use an attic fan.

    The only time I would ever use an attic fan is if I had a roof that was unusually difficult to vent passively; for example, if you had a hip roof. Hip roofs are tough. Those are the ones that sort of go up like a pyramid with a little flat part on top.

    LESLIE: Mm-hmm.

    TOM: With a hip roof, you can only have a very narrow ridge vent. Situation like that, I may use an attic fan but I’d make sure I have plenty of wide-open soffit vents so that I make sure that I’m not depressurizing my house.

    LESLIE: The house itself.

    TOM: But if you have your average sort of gable roof where you have a wide ridge and a nice soffit that overhangs, I would put a ridge vent and a soffit vent and let those work together to flush out the hot air in the summer and the cooler air in the winter.

    SCOTT: Well, I have ridge vents. That’s the one on the top, right?

    TOM: Yep.

    LESLIE: Yeah.

    SCOTT: OK, I already have those.

    TOM: But do you have soffit vents? Do have soffit vents at the overhang?

    SCOTT: OK, yeah. I’m pretty sure.

    TOM: Well, that would be important to know because you want to have fully-open soffits and fully-open ridges and let those work together. Because what happens is air – as the wind moves over your house, it will be drawn out at the ridge vent and pushed in at the soffit vent, go up underside the roof sheathing and cool it in the summer and take the moisture and the cold air out in the winter.

    SCOTT: OK, well great. Well, thanks so much.

    TOM: You’re very welcome. Thanks so much for calling us at 1-888-MONEY-PIT.

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