bathroom duct defective (MOLD)

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Old 05-08-12, 05:12 PM
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bathroom duct defective (MOLD)

I just discovered that the flex ducts for the ceiling fans up in both 2nd floor bathrooms were passed (up in the attic) out above the drywall ceiling but under the insulation and directed into the soffits. The moist air has obviously blown back up into the attic because the 2 bays directly above those soffits have black mold growing. I will rectify the mold issue, but have questions about the best way to properly vent those ceiling fans.
I could use rigid metal and go straight up and through the roof and add a roof vent. The attic is well insulated and air circulation is good; flows in & out proportionately and temps seem comparable (little warmer) to outside air. But I'm worried that sending moist air up this pipe will cause condensation in the winter months, and that condensation will follow gravity, drip back down and create ceiling problems around the fan. So my other option is to still use rigid duct and go up from fan, make one 90 degree turn and go to the rear of the house & install a through-wall (louvered) vent.
Are my concerns real about going up through the roof and causing the condensation a possibility/ does that happen?
Is the 2nd choice 'better' to help reduce that condensation buildup?

Thanks
 
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Old 05-08-12, 05:30 PM
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I'm no expert, but I just had a house with a full HVAC job done. My guy vented the "fart fans" with a combination of flex and ridig straight through the roof.
 
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Old 05-08-12, 06:37 PM
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I suggest the shortest and smoothest duct out the roof you can make. Then insulate the duct. Run the fan DURING the shower and continue running for several minutes AFTER the shower.
 
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Old 05-10-12, 07:36 AM
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Thanks for the input; everyone in the family always run the fans during showers, then leave them on for 1/2 hour afterwards.
And I had forgotten to say that I planned on insulating the rigid duct. But I am still wondering if going straight up vertically is 'better' than making one 90-degree turn & going out horizontally to the rear of the house & out through the vinyl siding....??
 
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Old 05-10-12, 07:53 AM
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How far will the horizontal run be?

I think it's better to go the shortest distance possible as well. One of my bath fans goes straight up about 9 ft almost to the peak of the roof and I've never had any problems

You said the existing duct was directed into the soffit? Was it just blowing AT it...or was a vent installed THROUGH the soffit to the outside? Something like this?

http://www.ntsupply.com/images/produ...3w.220x220.jpg

or this

http://www.ntsupply.com/images/produ...5w.220x220.jpg

Were the vented soffits on each side of the duct blocked off? I've seen fans vented though the soffit and if the above steps are followed...they normally work ok. I still like straight up and out or a through the wall better though.
 
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Old 05-10-12, 08:56 AM
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Venting through the soffit is the least desirable choice, regardless of how it is done. If you can run through a sidewall using less total run of duct than going through the roof then do the wall. Bottom line is to run the least amount of duct and have it be the smoothest (inside) that you can find. Length is far more important than is orientation.

Also, don't "choke" the fan by using too small a duct. Even if your fan has a 3 inch discharge connection use no less than 4 inch duct; adapter fittings to change size are readily available. Tape all seams/joints with FOIL tape, not the cloth-backed "duct" tape. That "duct" tape is NOT suitable as it dries out in a couple of years and falls off.
 
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Old 05-14-12, 08:52 AM
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Thanks to all; the current flexible duct is 'vented' by simply having the duct pointed down towards the vented soffit(NOT through the soffit); soffit & surround area is not blocked so air can flow freely. Unfortunately due to this poor placement & common knowledge that hot air rises, it vents the moist air UP onto the inside of the roof sheathing, causing mold.
When fixing this cheap install by builder, I already planned on matching the fan discharge with rigid duct of same diameter, and already have the foil tape and duct insulation. My biggest concern is the possibility of creating more condensation by going vertically off the fan discharge straight up through the roof (about 10 ft) or by going out the back wall of the house by putting in one elbow for that 90-degree turn. That decision would result in running about the same length of rigid duct- about 10ft.- just not vertically. This 2nd choice seems (to me, just a DIY-er) like it would (possibly) produce less condensation since the moist air isn't being pushed as far vertically and less chance of water dripping back down the inside of the duct. But that decision is only from a common-sense approach and not from any expertise, so please weigh in...
 
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Old 05-14-12, 09:22 AM
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I'd probably vote for straight up....warm air rises right? If the fans run after showering as you said...shouldn't be an issue.

IIRC a 90 degree bend adds 10ft to the effective length of a duct. Yep...quick check says you must reduce the max by 10ft if a 90 is in the line. That was for a dryer...but I'd imagine a bath fan is the same.

If you do the horizontal make sure it slopes slightly to the outside.
 
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Old 05-21-12, 05:41 PM
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UPDATE: I just had a visit from an alleged specialist at mold mitigation and he quoted a price above $1500 to wash off the mold and then clean up/remove the debris so no mold spores sprout anywhere else.
Well, without trying to insult the profession of someone who does something that I don't for a living, I considered this estimate to be a little pricey. I had already planned on laying out plastic sheeting myself to catch/dispose of any removed mold, and I could wash off the mold-affected roof sheathing myself, with protective mask, eyewear & a disposable suit....all for about 1/4 to 1/5 of the quoted price. Quotes are subjective-depends on certifications, territory/geographical area, equipment used, training obtained, etc. But does this estimate sound a little high to anyone else...?
 
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Old 05-21-12, 11:18 PM
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My sister bought a bank-owned house that had some minor mold issues due to a water leak. The first estimate for remediation came in around $7,500. The second estimate was less than half that amount. I suggest that you get several more estimates.
 
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Old 05-23-12, 07:36 AM
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thanks Furd.
dumb question but I have to ask it: before the word "mitigation" was coined, what did people do about mold? Progress is always good and safer methods are continuing to appear for everything. But why can't I roll plastic sheeting over the insulation in my attic, don protective apparel and wash the surfaces off with a mixture 5 parts bleach/1 part water, then secure the plastic containing mold debris and dispose of it myself?
 
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Old 05-23-12, 07:51 AM
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or- since it's such a small area (maybe 30 sq.ft.)- why wouldn't I just use any of the methods I found listed right here on this site at
5 Easy Ways To Remove House Mold | DoItYourself.com
?
 
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Old 05-23-12, 12:34 PM
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I don't know what the accepted methods for mold removal are and I wasn't present when the company my sister used started the process. I do know that when they finished whatever they did as far as removal they sealed all the surfaces with some kind of coating that looked to me to be nothing more than white pigmented shellac and then ran dehumidifiers and HEPA filters for the next several days in the otherwise closed house.

My feeling is that the area should FIRST be contained using heavy (6 mil minimum) plastic sheeting and then set up the HEPA filters inside this containment. Then using proprietary chemicals kill and remove the existing mold and seal the surfaces. Of course the person actually doing the work needs to take all the necessary precautions concerning throw-away coveralls, gloves, booties, respirators and such.

As for your particular situation...I cannot offer any more advice. You will do what you will.
 
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Old 05-24-12, 04:39 PM
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"...You will do what you will."
I will select a method suggested by this website and will follow those instructions
 
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