Ba. fan water damage

[kfc510]

This is at the site I'm on. Not my work, not my problem, but I can only pretend to not see it for so long...

Any tips/guesses on the likeliest problems? Kinda hard to diagnose over the net, of course.

First floor bathroom ceiling in an old 2-story house. Newish Panasonic fan. Unknown ducting. Bay Area climate. I believe (but am not certain) that the room above is a bedroom.

Any W.A.G.'s out there?

[rogerg]

Re: Ba. fan water damage

One guess would be that the moist air is condensing in the ductwork and running back. You want the condensing to take place 'after' it leaves the house. Maybe too much vertical and/or not enough insulation around the duct.
Just guessing.

roger

[parkwest]

Re: Ba. fan water damage

I concur with rogerg...

[kfc510]

Re: Ba. fan water damage

Yeah, condensation running back down the pipe was my guess too, although in this climate (and given that the duct seems to run through an interior joist bay) I wondered about that.

How would you approach diagnosing the issue? Pull the fan unit? Open up the ceiling to see the duct? Explore from the exterior?

edit to add: Roger, you mentioned "too much vertical". How does that contribute to the problem?

[FesFool]

Re: Ba. fan water damage

I have the same damage with the same fan, fortunately I primed the drywall before caulking around the fan so the damage is between the primer and the paint not in the drywall. And yes there was not enough insulation around the fan for an unheated attic in a cold climate. Not the same situation as yours.

Dan

[rogerg]

Re: Ba. fan water damage

Heavy moist air goes up at a slower rate than horizontal. It stays in the ductwork a little longer and increases the possibility of condensation. Usually any condensation in a horizontal run, runs out of screw holes or seams into insulation where it eventually dries out without anyone knowing. On a verticle run you will notice water pretty quick.
Sometimes if the customer leave their fan on for a longer time it will evaporate what is in the horizontal duct.

roger

[kfc510]

Re: Ba. fan water damage

Heavy moist air goes up at a slower rate than horizontal. It stays in the ductwork a little longer and increases the possibility of condensation. Usually any condensation in a horizontal run, runs out of screw holes or seams into insulation where it eventually dries out without anyone knowing. On a verticle run you will notice water pretty quick.
Sometimes if the customer leave their fan on for a longer time it will evaporate what is in the horizontal duct.

roger

Interesting. I would have guessed that the hotter air would benefit from rise, and that excessive run would be the problem. But I can certainly see how a vertical run would dump the most water back onto the fan housing.

kevin

[tomthetoolman40]

Re: Ba. fan water damage

I also agree with Rogers diagnosis. I have seen this numerous times when the run is long vertical. Whenever we install one we make sure there is a dip after the initial rise for moisture to collect in, then can evaporate out later, instead of draining back into the bathroom.

[kfc510]

Re: Ba. fan water damage

I also agree with Rogers diagnosis. I have seen this numerous times when the run is long vertical. Whenever we install one we make sure there is a dip after the initial rise for moisture to collect in, then can evaporate out later, instead of draining back into the bathroom.

Is there no concern for Legionairre's, bacterial growth, etc with trapped water? Or is that only a threat in a duct that is pumping air back into the living area?

[dgbldr]

Re: Ba. fan water damage

Is there no concern for Legionairre's, bacterial growth, etc with trapped water?

Not any more or any less than the trap under your sink, under your shower and a few other places around the house.

[kfc510]

Re: Ba. fan water damage

Not any more or any less than the trap under your sink, under your shower and a few other places around the house.

Yeah, but those are getting flushed on a pretty regular basis.

A mini pond in a duct seems different. I guess it's a minimal amount and would evaporate before any major problems. And whatever funk is in the duct shouldn't be backdrafting through the fan much anyway.

I dunno, not my area of expertise, obviously. It does seem odd to me to purposely create bellies or leaks in a duct to deal with the issue.

[MarkMc]

Re: Ba. fan water damage

If you got "mini-pond" issues then you may have need to address the installation and that will vary by site condition[s]. If there is a regularity of ponding [a condition that isn't readily rectified by an additional 10-20 min on fan cycling or natural venting over slightly longer time] then that would be a problem that should be fixed by a proper install that address the excess correctly - is it uninsulated duct? too long a run with a negative pitch? too small a fan? sticky/restrictive damper[s]? Properly executed it's not creating a pond, just preventing illiberal trickle down.

[kfc510]

Re: Ba. fan water damage

All good thoughts, Mark.

(The pond comment referred to the purposeful creating of a catchment dip in the duct, as mentioned above by Tom the Toolman. No one actually suggested drain holes, but Roger did note that horizontal runs may have fewer issues because water can drain out of screw holes in horizontals, whereas it just runs down a vertical to the fan housing.)

[kfc510]

Re: Ba. fan water damage

Dug up this similar thread.

http://forums.jlconline.com/forums/s...question/page2

kevin

[S.Joisey]

Re: Ba. fan water damage

Insulation around the vertical rise will minimize the temp difference and condensation, and rigid duct sloped to the outside will drain rest.