# Bathroom fan outlet freezing at roof



## Highbeam (Jan 3, 2011)

We've been frozen here for over a week. A few inches of snow still covers everything including my roof. Temps in the teens overnight. I have a bathroom fan that sucks air from the room, then through a one way checkvalve near the ceiling, up through an insulated duct, then hits the roof vent stub where another one way check valve exists, and then the steam blows out onto the roof and melts snow, makes visible steam etc. We shut off the fan after 30 minutes or so. 

The dang check valve on the roof freezes shut overnight so in the morning when I turn the fan on, it is unable to exhaust the moist hot bathroom steam air. My dang mirror fogs up. One time I was standing there when it broke free and began to work but the next day it was frozen shut again.

How do you folks up north deal with this? Is this common? Is my install faulty? 

I have a real outside air connection for the stove so house RH is perfect at 30-50%. I do not plan on just letting the steam dissipate into the home, that's why I have the fan.


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## Jack Straw (Jan 4, 2011)

I had the same setup for years. The hot moist air would travel up the vent hose towards the roof and condense in the cold attic. The water would then run back down and drip out of the exhaust fan onto your head. There was no access to the attic until I had the wood stove installed. After I had access I ran the vent hose under the attic insulation and installed a vent in the sofit. No more problems.


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## PJF1313 (Jan 4, 2011)

Both of the bath exhaust fans in the house exit on the side wall (N. side)  So far (3 years here) they haven't froze shut, like out old house did - like yours.  The ducts run between the rafters to an exhaust vent - clothes dryer type with the check flapper.  Both fans also have a flapper in the housing also.

  I don't like they way they (didn't) insulate the ducting, but I am afraid of changing one of them (flat roof area) to an insulated duct.  I may try the other, but it doesn't get as much use, so it might be a mute point.

  Do you have access to the attic?  Maybe you can do like "Jack Straw" did with his, or do like they did with mine (but insulated?)

Good luck with the sticky flappers!

P.J.


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## gzecc (Jan 4, 2011)

I think the solution is to leave the fan on long enough so there is no more moist air. Could be a long time. A timer could be put on it.  If there is that much moisture condensing on the outlet the outlet air must be saturated.


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## wingman1776 (Jan 4, 2011)

Leaving the fan run for  bit will help to dry the vent. You can buy insulated flex duct to run the bath fans in that is what local code requires here for new construction. they also have said no flapper at the roof. You can install a hood with a bent outlet to stop down drafts from wind.


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## velvetfoot (Jan 4, 2011)

No help, but I also have a soffit vent that freezes periodically.  It's near enough to the bathroom window that I can open it up with a stick.  i think part of the problem is negative pressure.  I've also left my fan on for a while to free it up.  It's funny how you see many recommendations for a roof (vs. soffit) location of the vent-I can't see it where it's snowy.  Maybe if the fan put out more pressure, but that makes for a noisier fan.  Maybe you could take the fan grill off and pressurize the duct with the exhaust of a shop vac.  When free, as noted, run the fan for a while to dry things up.  Another problem you have is you can't see if it's open, although I'm familiar with the delayed vent opening sound.


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## Highbeam (Jan 4, 2011)

I suppose the solution will have to be to run it longer. Even room air at 75 degrees and 50% RH will condense on the cold vent though so I'm not sure if it will work. Kind alike the cold coke can always gets condensation on it. 

I do have insulated duct and the run is pretty short so the steamy air is getting to the vent as warm as it can be when the vent flap isn't frozen shut. I can't imagine no flapper at the roof. Seems the bathroom fan would act like a big chimney then sucking hot air out all the time. The flapper at the fan assembly is hokey at best. 

I like noisy fans and more power would probably do the job. I'm already overfanned for the room size though and the install is sealed in. These fans are squirrel cage fans so when they stall they just spin making a slight huffing sound. Oh well, things will melt in the next few days as a warm storm rolls in. I was hoping that someone knew of a liquid that could be sprayed on the flapper to prevent freeze up. Like a silicone lube or something.


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## gpcollen1 (Jan 4, 2011)

I hear you but i don't use the fan in the winter.  I like the extra moisture in the house and don't want to exhaust my heat.  I only use the fan in the summer really.

I don't have any issues with foggy mirrors in the winter either...


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## semipro (Jan 4, 2011)

My local home centers carry inline check valves for 4" hose.  
http://plumbing.hardwarestore.com/5...ories/draft-blocker-inline-damper-602022.aspx

You could remove the flapper at the roof and install one a few feet down in the attic where it wouldn't freeze.   Its same concept as a frost free exterior hose bib (move the valve to an area where it won't freeze).


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## maverick06 (Jan 4, 2011)

mine vents out the soffit. What about if you spray the little hinge in the check valve with wd-40? that will help keep water off if it (what wd-40 does). Of course it will help dust stick to it, so maybe that makes it more annoying (go and clean twice a year), but its a thought. 

I run mine a long time after we take shous (hour plus) but still get some condensation on the cieling, espically near the outside wall.... not great.


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## Highbeam (Jan 4, 2011)

To really fix it, that remote flapper valve would be the ticket. Not sure how hard it is to remove the existing roof flapper, it is in behind a mesh screen


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## velvetfoot (Jan 4, 2011)

I've had that mesh screen clog up with lint over the a period of years.


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## Black Jaque Janaviac (Jan 4, 2011)

I've got almost the exact same problem.  I can tell it gets clogged because there is no melted snow by the roof vent.

I'm thinking that maybe just a slight kink or bend on that flapper could allow just some exhaust to come out.  Then with a slight current of warm air travelling through the vent perhaps that would be sufficient to thaw the rest of the flapper within minutes.  

Otherwise I'll try the silicon spray idea.

As for foggy mirrors - I soak a rag in hot water and sloooowly wipe off the fog.  The heat from the rag warms the mirror enough that it doesn't re-fog while I shave.


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## billb3 (Jan 5, 2011)

I guess my dad had the same problem with his. He not only got the  flapper valve for inside, he eliminated the roof penetration and plumbed it into the DWV in the attic just before it goes outside.  Probably not code.


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## midwestcoast (Jan 5, 2011)

+1 for the in-line flapper & removing the one at the outlet. Try to find a quality one. Most I've seen are cheap & crappy.
I dislike outletting to the soffit or through wall just below soffit if there are soffit vents around since those are intake vents & the ridge or mushroom vents are the exhaust. So putting the bath fan outlet at the soffit means the warm, moist air gets sucked into the attic.


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## fbelec (Jan 6, 2011)

Black Jaque Janaviac said:
			
		

> I've got almost the exact same problem.  I can tell it gets clogged because there is no melted snow by the roof vent.
> 
> I'm thinking that maybe just a slight kink or bend on that flapper could allow just some exhaust to come out.  Then with a slight current of warm air travelling through the vent perhaps that would be sufficient to thaw the rest of the flapper within minutes.
> 
> ...



+1  i think i will use that idea on my next install. cut a small hole with wire cutters or slightly warp the flap with pliers.


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## Black Jaque Janaviac (Jan 9, 2011)

GAARRR!

I went up on the roof, put a slight kink in the vent flapper.  Still no airflow.

Next I went into the attic and checked to see if the pipe had become disconnected.  

Now I suspect the vent pipe is plugged with frost.  The pipe was properly connected both at the fan and the roof vent.  But the flexible pipe was set up and runs over the air conditioner then drops down to form a "U" before connecting to the roof vent.  I felt this "U" and it feels heavy - like it was full of ice.  

I turned the bathroom fan on, returned to the roof, and could feel no draft whatsoever.  I was hoping if it had just a trickle I could run it to melt/evaporate it out.  

Any suggestions?


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## Highbeam (Jan 9, 2011)

You've got a trap in your vent line. It almost certainly is full of nasty water or ice. Either one would plug it and prevent the fan from blowing. Short runs are important with this vent line because you want the steam to blow out before condensing or else it will run back into your bathroom and drip. 

Biggest thing is you need to straighten out that trap. The contents will pour out (unless frozen) so be ready. Somehow keep the trap out by better bracing and strapping. Maintain that upward grade. 

A less desirable solution is that you could poke a hole in your vent line at the low spot, position a bucket under the hole to catch the deluge and then the future drips. Keep the bucket from overflowing.


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## Black Jaque Janaviac (Jan 9, 2011)

Oh it's frozen alright.  So what then?

Unfortunately whoever owned the house before us must have thought that a 2-story house still needs the vents on the back side of the roof.  The bathroom is on the front side - so a short run will be tough to arrange.  

I'm not sure if there was any wisdom is squeezing the vent pipe between the air conditioner and the rafters, but it seems like it would be easy enough to run the bathroom vent under the air conditioner and then up.  This would result in a rather long horizontal run, but should eliminate the trap.  

I think the other thing I'll have to do is instruct the family to run the fan for at least an hour after the last shower.


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## FordMastertech (Jan 10, 2011)

I was having the same issue with both of the bath exhaust fan vents when they were vented into the soffit area. I removed the 1X12 solid boards that were in the soffit and replace them with the Certainteed hidden vent vinyl soffit so I didn't want to vent the fans to the soffit area any more or through the roof as I really don't like anything coming out of the roof or making holes in it. I ran the new vent lines using the 4 inch thin wall ABS white drain pipe to the southern gable end of the house. The pipes come up from the fans on a 45 degree angle and use a 45 degree elbow to connect to the horizontal run that is pitched slightly to the gable wall to provide drainage to the out side of the house. There is a simple dryer type vent on the gable wall now. The pipes are uninsulated in the attic and have about a 20 foot run from the fan to the gable wall. They haven't froze yet this year.


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