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Jim Dull
03-02-2008, 07:03 PM
I received an email from a fella asking for some help. I would like to help him but would like input from some of you. He is having occasional leaks of water from the ceiling near and around AC vents and light fixtures.
Jim Luttrall
03-02-2008, 07:41 PM
Look for condenstation on the metal ducts. If insulation is lacking and humidity is high enough, it will collect and drip onto the ceiling around the grills.
Eric Barker
03-02-2008, 08:07 PM
Jim D. - When air can pass into a cold attic through ceiling penetrations the moisture in the air condenses out on the metal parts. Around here that's metal conduit and J boxes. It may not seem like a big deal to some people but it can create quite a bit of water. The same can be true of metal ducts. It can be controlled by trying to seal up the penetrations and making sure insulation is adequate.
Matt Fellman
03-02-2008, 08:54 PM
This is pretty much what the others said but, taking it one step further, the bath fans in particular can cause water to run back down the ducts and drip from the attic. I've seen it come through light fixtures, heat ducts and other places.
Nolan Kienitz
03-02-2008, 10:38 PM
... the bath fans in particular can cause water to run back down the ducts and drip from the attic. I've seen it come through light fixtures, heat ducts and other places.

And just where are these bath exhaust fans routed? Do they just terminate in the attic or are they truly "outside" the structure ... and I don't mean just dumped into the soffit vent/eave area?

What type of vent pipe is used for the exhaust vent? Are you saying that the bath exhaust vent pipe is causing the condensation to appear around the fixtures?

I think Jim's input RE: insulation & humidity is pretty much right on.
Jerry Peck
03-03-2008, 07:43 AM
I think Jim's input RE: insulation & humidity is pretty much right on.

And Eric's explanation if also pretty much right on, for the reasons Jim said.

Warm moist air from inside rises ... hits cold metal because of no insulation ... equals "condensation" ... condensation equals water ... water runs downhill ... gravity wins. :)