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Bathroom exhaust fans vented through the soffit. Water drips down all the time.

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  • Mar 4th, 2018 2:53 pm
[OP]
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Jul 12, 2015
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Bathroom exhaust fans vented through the soffit. Water drips down all the time.

New exhaust fans were put in to my bathrooms that never had any exhaust fans previously. The contractor chose to vent them through the soffit. Every time someone takes a shower, water drips down from the fan and puddles underneath it. He claims that it's because I don't have enough insulation in my attic, and there is not much that he can do about it.

In researching this, I find that bathroom exhaust fans should NOT be vented through the soffit, especially if the soffit already has existing vents in it for airflow. All that does is allow the moist warm air from the fans to go back into the attic and cause rot and mildew. Also the bends in the duct to go from the fans to the soffit vents would also trap the moist air and it condenses back into the water that I see on the floor after every shower. It is always better to vent straight up through the roof.

Could there be any other reason for this dripping water? Thanks for any advice.
23 replies
Member
Jan 7, 2013
414 posts
175 upvotes
Whitby Ontario
Venting through soffits isn't ideal but it can work. I did the same project myself on a bathroom with no fan.

Use insulated flex ductwork (but keep it relatively taut), attached to port from the fan which is horizontal, slope duct towards to the soffits, and use a hood that directs the air away from the home instead of straight down.

(I used panasonic fan with this hood https://www.primexfits.com/hvacventing/ ... ut-screen/ for 12$ from Noble in Oshawa)

Is your fan box itself cold? Mine is buried under 18 in of insulation. Maybe your metal box was left exposed and it's condensing inside air.

Otherwise unless your duct is sloped backwards I don't think you'd be getting water back into the house.
[OP]
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Jul 12, 2015
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Both fan boxes are buried under several layers of that pink batting insulation. The soffit vents from the fans have the air going straight down. There is nothing directing the air to go away from the house. I will have to go out there while the fans are running and take a second look. The problem is that there is already an existing soffit vent for the attic right next to the vents from the fans. All along that section of the soffit, there are three other pre-existing vents. I am waiting to hear back from the contractor on why he chose to vent this way instead of through the roof.
Jr. Member
Nov 25, 2007
146 posts
44 upvotes
Ottawa, ON
So, the hot moist air is going in the vent, and condensing into water when it hits the cool duct work and then dripping down through the fan?
Member
Jan 7, 2013
414 posts
175 upvotes
Whitby Ontario
I blocked the closest soffit vents to my exhaust hood (My entire soffit area is vented). But the fan with the directional hood seems powerful enough that the air it blown clear away.

I've looked in my attic during the winter and no signs of frost etc (yet anyways).

All the new build homes near me are using soffit exhausts....for better or worse.
Sr. Member
Jan 14, 2010
640 posts
180 upvotes
Central Ontario
We had this problem as well, and chose to reroute the venting through the roof after we realized the builder had taken this shortcut. The dripping is one thing, more important is the mould risk that is very real.
We did exactly as google suggests: insulated piping to an installed roof vent. It was a PITA, but glad we did as I see neighbours with mould/mildew on their soffits/gutters.
Deal Guru
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Feb 11, 2007
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Oakville
You're right, the vent should not exhaust into the soffits. You could have someone install it properly through the roof. Either way, the vent tube should be insulated to prevent condensation. The exhaust in soffit should also have a flap that is closed when the fan is off.
Deal Addict
May 9, 2003
1110 posts
269 upvotes
For a temp solution you may want to run the exhaust fan at least another 20-30 mins after the shower to help "push" the moist air out.

Though I believe the moist air is getting "stuck" in the bends in your ducting.

I would also suggest insulating the duct if not already as a first try.
Member
Nov 30, 2015
319 posts
139 upvotes
GTA, ON
AlexiRos wrote:
Mar 1st, 2018 7:55 pm
Both fan boxes are buried under several layers of that pink batting insulation. The soffit vents from the fans have the air going straight down. There is nothing directing the air to go away from the house. I will have to go out there while the fans are running and take a second look. The problem is that there is already an existing soffit vent for the attic right next to the vents from the fans. All along that section of the soffit, there are three other pre-existing vents. I am waiting to hear back from the contractor on why he chose to vent this way instead of through the roof.
Yes, it's a good idea to go outside and take a look at the vent while the fan is running to see if the flaps on the vent actually opens up when the fan is running. The vent I installed myself looks like the picture below. I had a problem with the flaps opening even with a fan rated at 80 cfm. Why? The spring to keep it closed was just too stiff and seemed to require a fan with a lot more cfm air output to push it open. My only solution while not ideal was to stretch the spring a bit to weaken it.

vent.jpg
Member
Jan 7, 2013
414 posts
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Whitby Ontario
lazybummer wrote:
Mar 2nd, 2018 11:02 am
Yes, it's a good idea to go outside and take a look at the vent while the fan is running to see if the flaps on the vent actually opens up when the fan is running. The vent I installed myself looks like the picture below. I had a problem with the flaps opening even with a fan rated at 80 cfm. Why? The spring to keep it closed was just too stiff and seemed to require a fan with a lot more cfm air output to push it open. My only solution while not ideal was to stretch the spring a bit to weaken it.


vent.jpg
This is why I liked the hood I linked above. It blows away from the house, and you can easily tell if the flap is opening. Only downside is some might not like the appearance of it. But function is better over form, I think.

And if it freezes shut, I can whack it with a broom, lol.
[OP]
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Jul 12, 2015
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lazybummer wrote:
Mar 2nd, 2018 11:02 am


vent.jpg
This is the exact same vent that the contractor has put in at my house. The Panasonic Whisper Ceiling Fans rated up to 110CFM were installed. Not good to know that even with your 80 CFM fan, the flaps aren't opening.
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Thanks for all the feedback and shared experience. So far the contractor has refused to address why he chose to install the exhaust vents in the soffit instead of the roof. He just kept emphasizing that it's because I don't have enough insulation in my attic. He had said that both insulation and a vapor barrier were put around the exhaust ducts.
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Feb 11, 2007
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AlexiRos wrote:
Mar 2nd, 2018 12:01 pm
Thanks for all the feedback and shared experience. So far the contractor has refused to address why he chose to install the exhaust vents in the soffit instead of the roof. He just kept emphasizing that it's because I don't have enough insulation in my attic. He had said that both insulation and a vapor barrier were put around the exhaust ducts.
It should also be rigid/semi-rigid tubing because that flexible mylar stuff sucks. It's higher resistance and can easily be crushed to restrict flow.
[OP]
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engineered wrote:
Mar 2nd, 2018 12:07 pm
It should also be rigid/semi-rigid tubing because that flexible mylar stuff sucks. It's higher resistance and can easily be crushed to restrict flow.
I am pretty sure that he used that flexible mylar stuff. I remember seeing some silver, mylar ducts with his work tools.
The more I learn on here, the more I think that I am either dealing with an inexperienced contractor or an unethical one.
Newbie
Jul 5, 2006
72 posts
17 upvotes
Burlington
Go with the Primex sofit vents they have no restriction, sofit venting is not the best personally a roof vent is better. Also any ductwork should be insulated in the attic
Last edited by photoads on Mar 2nd, 2018 5:50 pm, edited 1 time in total.

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