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Recently had a guy come out to clean the clothes dryer and clothes dryer vent. Asked him to clean out the bathroom fan vent as well. He looked up the attic, on the roof, and along the siding, and could not figure out to where it vents out. I would think it would be obvious, but it's not.

I opened up the fan and it is attached to ducting. I'm concerned that the ducting might go straight up into the attic and terminate under the attic insulation. I have an injury, so I haven't wanted to go up there and start tearing away insulation unless I really need to.

Is there a good trick to figuring out to where a bathroom fan vents out?

  • have a guy shout in the vent and listen on the other side (assumes it's reasonably clear) – ratchet freak Nov 5 '14 at 11:25
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If you have access to the attic; and presumably the top of the bathroom fan, you may be able to follow the duct.

If you don't have access to the top side of the fan, you could remove the cover and take a peek inside. You should be able to get a glimpse of the outlet, which should allow you to determine if there's ducting attached.

In my house, the bathroom exhaust fans vent directly into the insulation around them (an issue I've been meaning to fix since I moved in). Because of this I don't use the fans, since I'd rather have the moisture in the conditioned space than in the insulation.

If you've determined that there is actually ducting attached to the fan, you could use a fog machine to help locate the outlet.

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You can usually pick these up fairly cheap; especially around Halloween, or possibly rent one from a party supply store. Set the machine up in the bathroom, and turn on the exhaust fan. Then walk around your house looking for the fog.

NOTE: You might want to set the fog machine up on a ladder, as close to the exhaust fan as possible. Otherwise you might have to fill the entire bathroom with fog, before it's actually sucked into the exhaust fan. The fog tends to be heavier than air, and so tends to hang around the floor.

Smoke pellets, smoke candles, and other smoke testing devices are also available. Which may work better than a fog machine, since the smoke from these are typically lighter than air.

The product links are for demonstration purposes only, I have never used these specific products and do not endorse nor recommend these specific products.

  • Thank you for the ideas. Your bathroom exhaust was built to vent directly into the attic insulation??? That's exactly what I'm concerned they did in my case too. I haven't wanted to get covered in fiberglass ripping up the attic insulation to figure it out. I wonder if there are any building codes for this sort of thing. BTW, the fan exhaust is definitely attach to ducting. – RockPaperLizard Nov 5 '14 at 19:15
  • There are building codes that say it's supposed to be vented outside. Unfortunately these codes seem to have come after bathroom fans became popular, so it's not uncommon to find them venting to nowhere. If the installer took the time to install a duct, it's likely that it went outside at one point. However, another common exhaust fan mistake is to vent it out the eaves. If there's a duct connected, but no visible outlet outside. It's possible yours vents out the eaves, which is usually not so good. – Tester101 Nov 5 '14 at 20:57

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