Am installing a fan/light unit in the ceiling of my 2nd floor bathroom. Can I run an insulated flex duct directly into the attic and terminate it so it exhausts into the opening of an existing roof vent (the square aluminum type that is installed when a roof is shingled). or do I have to cut in a new vent opening specifically for the fan?
Thanks, advisors!
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Tom, that you are trying to do it better than some builders who just throw the hose up in the attic to let it spew is good. I would vote for the new vent out the roof if that's where you have to go. You have a dedicated route with an additional flapper to stop back draft. In a cold climate the warm moist air surely will condense and flow back the pipe if not insulated. I have taken to using hard pipe from fan to roof with it's own vent hood if unable to run to an outside wall. I have sleeved it in flex insulation and even just wrapped it with fibreglass with a vinyl wrap. I don't think there's much more you can do to eliminate condensation. Some have used pvc which might slow condensation down. Never tried it. best of luck.
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Remodeling Contractor just outside the Glass City.
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A few months after buying my house 18 years ago, water began falling from the fan following a steamy shower. I went up into the attic and found that the builder had nailed the accordian plastic hose under the gable vent (the wall was about three feet away.)
I had to rout out a square opening through the cedar clapboards for the trim (I'm anal that way) and used a 4" hole saw through the trim and sheathing for the vent hood, positioned below the level of the fan to ensure the condensate would drain out. (I also added a bird guard.) I replaced the hose with aluminum duct, and covered the whole arrangement with the attic insulation. I've done a number of these since, all the same way, and haven't had a problem with any of them. The fan is more efficient using smooth wall duct with short runs and a minimum of bends.
BTY, I wire them up with 15 minute timers. Kids have a habit of turning them on and forgetting about them, which is a waste in the winter. As a side benefit, I've told my kids that when they shower, when the fan stops, then their shower is over (after rinsing.) It only takes once or twice shutting off the hot water to reinforce it, and they've been great ever since.
Tom, Calvin is right. The exhause fan would be best to have its own opening out the roof, I think they sell kits @ the orange HD store, and the shorter the distance the better. I seen a house that had run the vent too far and all the vent did was fill up with water and leak back down onto the ceiling. But using the insulated duct is a good step in the right direction.
Luck to ya