Repairing Attic Fan? Don’t Bother!
LESLIE: Rob in Massachusetts, you’ve got The Money Pit. How can we help you today?
ROB: So my wife and I just bought a brand-new house. And when we first got there, I turned on a light switch and our fan in the attic started smoking. So I went up there. It looks like it’s the back of a submarine. It looks like this really big, old, propeller-driven fan, so that’s got to go.
So, as I’ve been doing a little bit of research online, it seems like there’s kind of two camps going on as to whether or not it’s really worth having an attic fan or not, whether it really saves energy and saves you money over time or if it’s really just something that’s kind of a legacy or holdover from a different era. So I guess I just want to get a take from that.
TOM: OK. So is your home air-conditioned?
ROB: It is not.
TOM: It is not. OK. So you’re using, what, window air conditioners in the summer?
ROB: Yep. We have window air conditioners up on the second floor. Down on the first floor, it’s actually been pretty cool.
TOM: So here’s the thing. You’re going to run this attic fan in the summer and I presume this would be one that’s repaired and not smoking. So let’s assume it’s operational. If you run it in the summer, what it’s going to do is it will depressurize the attic. Now, it’s going to try to make up that air from somewhere.
Now, theoretically, it would pull in air from other vents in the roof – other passive vents – like vents at the gables or vents at the soffits or other roof vents to be able to kind of take air from the outside. It will go in those roof vents, up through the attic fan and out and sort of just cycle.
Truth is, though, that those fans are usually a lot more powerful than the amount of passive venting available to make up the replacement air, so they’ll sort of reach down deep into the house and start pulling out air from your house and venting that, which they’re not really intended to do. They’re only really supposed to be venting the attic.
So, what happens in that scenario is they pull out not only the warm air in your house but the air-conditioned air, which is your expensive air that you paid to cool. And so that’s why they can be very inefficient, because they can rob air-conditioned air from the house: a bigger problem when you have central air than when you just have window units. But that’s why we generally don’t recommend them.
The other reason is that you really don’t need them. You could do just as good a job with proper passive ventilation. And by that I mean generally continuous ridge vents, that go down the peak of the roof, and soffit vents at the overhang. With that combination, air will always press in under the soffits, right up under the roof sheathing, and exit at the ridge. And it just does a good job, passively, of keeping the attic cool without impacting the cost of cooling or having attic fires because your fan motor blows up.
ROB: And then I guess, just to go off of that for a second, in the winter I’ve heard that you can run the attic fan in reverse and push the hot air that’s risen up into the attic down into the rest of the house. Is that also a myth?
TOM: That’s a complete myth. I wouldn’t do that. That would be – actually be foolish. You could mess with your – the natural ventilation, the natural draft of your heating equipment by doing that and it could be dangerous. You could build up carbon monoxide and cause fireplaces to backdraft. It could just be a real mess. So, yeah, I would not do that.
ROB: OK. Perfect. Thank you guys so much.
TOM: You’re welcome. Thanks so much for calling us at 888-MONEY-PIT.