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What's this bath fan water stain all about?

Updated: Apr 23

Ever notice this water stain along the edge of your bath fan? This staining is caused by warm humid air being ducted into the attic space on a cold day. The air will freeze inside the pipe and thaw when temps warm. This water will then travel back down the duct and end up on the ceiling beside the fan. An easy fix is to head up into the attic and create a "trap" with the duct so the water will gather at a downswing in the duct inside of falling all the way back down to the ceiling. The stain can be removed using a bleach/water mix in a spray bottle.

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