Condensation around bathroom fan vent..

[b7labelle]

Hey Everyone..

Noticed there was a small puddle of water in the light fixture for my bathroom fan. Pulled it down and it appears to be coming from the side of the fan. Went up in the attic and did not see any leak paths coming from the roof. I did feel moisture on the bottom of the vent tube coming out of the top of the fan in the attic, and only on the low spots of the vent tube where it was collecting.

I am trying to figure out if this is a ventilation issue in the attic as there are no baffles up and the blown in insulation appears to be covering all of the soffit venting. However this goes against what I understand about condensation. Water will condense on the warm side of 2 surfaces, given enough humidity. There is a joint in the vent tube where the water may be trickling out from, but there is a high spot where the drips would be unable to pass and yet there is still condensation on the bottom of the next low spot.

I'm thinking (hoping) this is just an ventilation issue. I think for 75 bucks at HD I can get the baffles I need.

 

[JakeKohl]

The attic is cold. Your bathroom is exhausting warm moist air into the cold exhaust pipe.
With the fan on, the moisture in the warm humid exhausting air is condensing on the inside of the exhaust pipe and draining back down to the light fixture.

I'm assuming the exhaust ducting for the vent is a rigid or single wall flexible pipe? It should be an insulated duct to reduce the temperature difference between the interior of the pipe and the exhausting air to reduce the condensation. If this is the case, you can probably fix by replacing the exhaust tubing with insulated tubing or insulating the existing exhaust tube.

It also sounds like ~maybe~ your bathroom exhaust is venting directly into the attic (can't tell exactly from your description) - it should not be this way...you don't want to dump hot moist air into the attic. This will lead to mildew/mold problems on the cold roof sheathing (assuming the sheathing is not directly insulated). The bathroom vent should protrude through the roof and vent directly to the great outdoors.

 

[b7labelle]

The attic is cold. Your bathroom is exhausting warm moist air into the cold exhaust pipe.
With the fan on, the moisture in the warm humid exhausting air is condensing on the inside of the exhaust pipe and draining back down to the light fixture.

I'm assuming the exhaust ducting for the vent is a rigid or single wall flexible pipe? It should be an insulated duct to reduce the temperature difference between the interior of the pipe and the exhausting air to reduce the condensation.

It also sounds like your bathroom is venting into the attic - it should not be this way...you don't want to dump hot moist air into the attic. This will lead to mildew/mold problems on the cold roof sheathing (assuming the sheathing is not directly insulated). The bathroom vent should protrude through the roof and vent directly to the great outdoors.

Ahhh did not think about that part of the puzzle. I'd have to task a 2nd look at the tubing...looked a lot like plain dryer vent, but taking a quick look on the Googler tells me they do look similar..

It appears to be venting through the roof properly..I'll have to take a 2nd look.

Baffles still suggested?

 

[b7labelle]

Just rechecked the attic tubing. Totally dryer venting. Single walled non insulated. There is a little loopty loop, the the whole bottom of that loop is filled with water. If I lifted up on it, I would have quite the mess in the bathroom....

Anyways...looks like I know what I'm doing tomorrow after work. Thanks!

 

[Scott H in Wheaton]

Baffles are always a good idea, but they aren't the source of this problem.
Insulated duct should solve it.
A stronger fan to push that moist air out would help as well.
Seems like the fan is just pushing it into the duct and its not getting all the way out through the roof vent.

 

[Nowater]

Also slope the vent towards the outside exhaust vent opening so any water that condenses runs out.

 

[b7labelle]

Baffles are always a good idea, but they aren't the source of this problem.
Insulated duct should solve it.
A stronger fan to push that moist air out would help as well.
Seems like the fan is just pushing it into the duct and its not getting all the way out through the roof vent.

I will be picking up an insulated duct and likely a stronger fan...fan didn't seem to be able to keep up with steam from shower..not even close.

I've been meaning to throw baffles up anyways...might as well do it now.

Also slope the vent towards the outside exhaust vent opening so any water that condenses runs out.

I want to make sure I'm visualizing this correctly...are you suggesting to run the hose like an inverted V, with the apex of the V above the exit vent on the roof?

Thanks.

 

[Scott H in Wheaton]

I will be picking up an insulated duct and likely a stronger fan...fan didn't seem to be able to keep up with steam from shower..not even close.

I've been meaning to throw baffles up anyways...might as well do it now.

When we insulate an attic our purpose of installing baffles between every pair of rafters is to force the guys to get to the edge of the attic and make sure every soffit vent is clear. Then, because we are going significantly higher than the original insulation the baffles are so our new insulation doesn't block all the vents we just uncovered.

If you have only a few inches of insulation existing and if you can see daylight coming in from your soffit vents you may not need to do the baffles. If however you have the USDOE suggested R49 - R60 then yes, you should get up there and do the baffles.

 

[JakeKohl]

Also slope the vent towards the outside exhaust vent opening so any water that condenses runs out.

I can't quite figure out how you achieve that unless you vent through a sidewall or possibly the soffit. Ideally, your exhaust goes through the roof sheathing. As long as you have an insulated exhaust duct condensation should not be an issue even with a vertical run. If you do vent through the soffit, make sure you don't have soffit venting back into the attic near the exhaust or all of that moist warm air will just rise and go right back into the attic.

 

[BillK]

B7,
I would not waste the money on the insulated ducts. I have never seen them used and I would bet it will not do a whole lot of good. Sounds more like you need to address the routing of the duct you have there now. Getting rid of the "loop" will probably solve most of the problem.

As far as the vents go, they certainly should be installed for better roof life, but if you think about it they will only make your current problem worse. The attic will be colder with the vents, making it more likely that you will get condensation in the duct.

 

[Jackfre]

If you change fans I would recommend the Panasonic brand. As well, I would use 4" AL pipe with appropriate fittings. Using the smooth wall will increase the performance of your current fam by reducing the pressure drop. If you want to insulate the pipe you can use duct wrap.

 

[JakeKohl]

B7,
I would not waste the money on the insulated ducts. I have never seen them used and I would bet it will not do a whole lot of good. Sounds more like you need to address the routing of the duct you have there now. Getting rid of the "loop" will probably solve most of the problem.

As far as the vents go, they certainly should be installed for better roof life, but if you think about it they will only make your current problem worse. The attic will be colder with the vents, making it more likely that you will get condensation in the duct.

You have to ventilate your attic space unless it is insulated behind the roof sheathing and becomes climate controlled space. Otherwise you get moisture build up, condensation, and mold. Moisture in your home migrates into the attic in the winter with or without vents pouring hot moist air into it. Unless it is climate controlled space as mentioned above, attic space should be well ventilated and at or near outdoor temperature in the winter. If the attic temperature deviates significantly from the outdoor temperature and you do not have insulated roof sheathing, you will have mold on the underside of the sheathing. I've experienced the mold issues that resulted from a previous owner thinking that buttoning up the attic in the winter would save them energy $.

Insulated ducting should be used because it should get cold in a properly vented attic space. Cold air around a duct with warm moist air inside will product condensate. Having or not having a loop will not change this (although the loop adds more surface area for the potential to collect more condensate). In cold weather climates (like the OP's) you should absolutely use an insulated duct for a bathroom exhaust fan and ensure that it is venting directly to the outdoors.

The only way to escape this need is to insulate the roof sheathing (usually with spray foam) and then heat and cool your attic as you do with the rest of the home.

 

[DekeT]

This problem might be solved by just running your fan longer to clear out more moisture.

 

[Nowater]

Sorry, I was thinking of my plan to vent through the soffit away from windows. If the duct runs downhill, any condensation will follow it down and out. Maybe you are venting straight up, is that the case? You confused me with the mention of the loop.

 

[b7labelle]

I would run the fan for 30 minutes after I was out of the shower with the door open. The fan probably wasn't evacuating any air because the vent was completely blocked with water.

Picked up replacement insulated vent at Hd for about 25 bucks.. 25ft or so. Cut about a 10 foot section and ran the shortest path I could from the fan exhuast port to the vent exit in my roof. Going to have to do the other bathroom 's vent in the future.

I'll also be putting in baffles in soon to help with ventilation in general.

Ended up taping the end tight after i took this photo:

old tube:

 

[JakeKohl]

that should take care of it!