Bathroom Exhaust Fan Ductwork & Moisture

Old 07-26-17, 08:08 PM
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Bathroom Exhaust Fan Ductwork & Moisture

My current situation is flex duct running from the exhaust fan upwards to the attic roof and peeling bathroom ceiling paint. My goal is to install the proper (recommended) duct work (and after paint repair), to ensure the ceiling paint will not peel again. Any offerings of advice,etc. is both welcome and appreciated. Thank you.
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Old 07-26-17, 08:23 PM
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Is it leaking moist air into the attic?
Old 07-26-17, 08:27 PM
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The best scenario (imo) would be to keep the entire duct low... have the duct running straight down the floor joists in the opposite direction, buried in insulation so the pipe stays warm (your attic is severely underinsulated) then a tee would be installed under the roof sheathing with a cap on the bottom portion of the tee (to catch and hold any condensation where it could eventually evaporate) and then duct up the tee a few inches into a louvered 4" Lomanco roof vent. And use solid pipe, not flex.

Or, if you prefer, duct it downward out the soffit, provided there are no soffit vents within 3 ft of it. The original paint was probably a gloss oil, since covered with latex and the two don't bond well.

I expect the paint is failing because of the cold underinsulated ceiling v.s. the high humidity in the bathroom ceiling and condensation after a shower.

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