Condensation Dripping From Range Hood Fan

 
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Old 02-23-2009, 03:07 PM   #1
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Condensation Dripping From Range Hood Fan


My mother-in-law lives in Oregon and emailed me the following question/problem. Since she's too far away for me to just hop on over and look at it, I thought I would post the question to you all. Here home was built in 1990 and is fully insulated with dual-pane windows and door.

"Ever since I moved in (nearly 19 years ago), when the temperature drops into the middle 20s or below at night and rises only barely above freezing during the day, I have condensation dripping from the range hood fan. I know this is condensation because no water drips during rain storms or even after snow storms unless it is cold. Because we don't have cold weather every winter, I don't have the problem every year. No one else has seen the problem because by the time someone could get here, the weather would have warmed and the dripping would have stopped. This winter for the first time water came between the cabinet and the range hood and dripped on the stove. In fact there was so much water, that I kept a towel on the stove to catch it. My handyman took the cover off the chase where the exhaust pipe is and could tell there had been water at some time by the staining on the floor of the cabinet. Several years ago, I had the pipe in the attic insulated but that didn't stop the problem."

I'm open to your thoughts.
Thanks!
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Old 02-23-2009, 03:28 PM   #2
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Re: Condensation Dripping From Range Hood Fan


The exhaust duct has too much pitch and the inside damper must be staying a little open.

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Old 02-24-2009, 03:31 AM   #3
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Re: Condensation Dripping From Range Hood Fan


Aloha Tom,
Thanks for your quick post/reply.
Since I am not onsite, I cannot view the actual pitch of the exhaust duct, but I will ask my mother-in-law tomorrow.
As for the flapper staying a little open, well, I will mention that to her too.
These things always make you wonder how one home in a tract has these issues when the others don't.
To anyone else out there, I would appreciate your opinion as well.
Thanks again!
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Old 02-24-2009, 12:15 PM   #4
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Re: Condensation Dripping From Range Hood Fan


the moisture is coming from the interior air and condensates where the hot meets the cold. So you have to stop the interior air from entering the duct period or from meeting up with the cold. Except when the fan is running, then it should heat up enough to exhaust the air and warm up the duct and not cause condensation.

So everything points at the damper or the insulation. A lot of exhausts are located along an exterior wall. With a hip roof, this space is almost impossible to reach from above. Has anyone seen the insulation on the exhaust duct? If insulated pipe wasn't used from the get go, I would think this is still suspect.

Otherwise, you've got the damper issue.

I don't see anything more than these two possibilities.
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Old 02-24-2009, 08:36 PM   #5
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Re: Condensation Dripping From Range Hood Fan


Tom,
My MIL replied, "I'll run it by my handyman next time I have him do some work. As far as I know, the duct goes straight up through the attic and through the roof. I can hear the damper move when the wind is blowing. "

Cleveman,
The exhaust duct was insulated after the fact, so it's probably not actual insulated ducting.
The location is in the near center of her home, not near an outside wall.
If she can hear the damper moving when the winds blow (and they do get extreme winds in the valley where she lives) then perhaps the damper is worn out or in a less than desirable position.

I will post again after she has her 'handyman' look at it.

Aloha!
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Old 02-24-2009, 09:02 PM   #6
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Re: Condensation Dripping From Range Hood Fan


Cleverman is right. Warmer air retains more moisture than colder air, so as you warm house air moves through the vent and meets the colder exterior air it reaches its dewpoint, thus the "leak". If you can keep the draft to a minimum you should be ok.

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condensation, range hood drips, vent condensation, water on range


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