Bathroom fan not venting

[andyvh1959]

I remodeled our main bath in 2018, which included replacing a sunken tub with a tub/shower combo. So my wife daily uses the shower and turns on the vent fan to reduce mirror fogging. Over time the ceiling around the fan in one direction starting peeling/flaking, so more repairs for me. Should say I've been in the house since 2002 and had no prior ceiling issues in the bathroom. So I assumed the ceiling fan was never properly vented.

Dug around in the attic above the bedrooms today and found there is ducting, about 18' long from the ceiling fan to the east roof eave vent. I ran a camera cable into the duct from the fan and found nothing but a bit of dust as far as I could reach in, about 14', no evidence of the ducting being rusted out. So I'm assuming the outlet end of the ducting is blocked with debris. So my next project is to remove enough ducting in the attic to confirm if the end of the duct need to be cleared to actually venting out the eave (note, I'm in Green Bay, typical Wisconsin winter weather). I can access most of the ducting except for about 8' that routes through a finished ceiiing of the bathroom, hallway and bedroom.

Assuming the end of the duct is blocked, so the fan vented out the less resistance gap in the ducting, which caused the bathroom ceiling plaster damage. Once I confirm the duct is cleared I may have to bust out a section of the bathroom ceiling to replace some ducting. Or, if there is a liner I can install into the ducting, like a thinwall plastic tube, I may avoid having to break open the ceiling.

 

[AC-WC]

Some other things to think about:
Has the wind been blowing and blocking the vent?
I would try running a fish tape from the fan to the exit hole.
Can you tell if vermin built or blocked the exit?
Did the 'seal' from the fan to the duct come loose?

 

[CraigStu]

Another option is to run the vent duct up to the ridge vent. Our previous house was done that way. It was 20 yrs old when we bought it and we lived there for 5 years and it worked fine.

 

[andyvh1959]

Have considered that as a better option. Though, that roof section on my house is a simple shed style, no ridge vent and the west side eave vent cannot be accessed. If I go up instead of to the eave I'll need to get on the roof and install a vent.

One thing though about my house and location is the possibility of deep snow. The roof section where the vent would be has only a 3x12 pitch so it is possble at times to have more than six inches of snow on the roof. That could be enough snow to cover a roof vent. The plumbing vent stacks on my house both extend out of the roof close to 12" for that reason.

I did notice the ducting to the eave vent stops short of the eave, and the ducting rises up at the eave end. So as warm bathroom exhaust air cools and condenses, and moisture runs BACK toward the fan or to wherever the system is lowest, which I bet is where I am seeing ceiling damage in the bathroom. I'll fab up a box to fit between the rafters with the bottom exhausting into the eave, so the fan duct can only exhaust into the eave and only where the box is. Right now the duct just ends above the eave.

 

[PCustoms]

@andyvh1959 where is the actual vent?

I used to have a pop out vent in the (non vented ) soffit, would get icicles and freeze up in the winter.

Since switch to a more appropriate outlet has not been an issue.

My fan is remote mounted in the unconditioned attic, if I don't let it fully remove the moisture after a shower it can freeze

 

[Jackfre]

Check the specs on your fan. Does it have the capacity to run against 18’ of duct. Is the duct smooth metal or corrugated plastic/metal

 

[PWC Repair]

Mine just blows about 2ft up into the attic. House was built in '58 and has a 36" gable vent on each side. I've been in this house 28 years and never had any issue.....no signs of wetness or mildew anywhere.

 

[Codyboy]

So for 16 years there was never excess moisture/hot steam in the bathroom until the shower install.

I'm assuming the attic is cold this time of year and warm in the house?
Did you check the insulation around the exhaust fan in the attic and the seal on the cover against the ceiling?
Maybe warm air is going up from inside and cold air from the attic is trying to migrate downward and mixing right there at the ceiling.

 

[75gmck25]

Older bath vent fans are very cheap units that do not vent very well. They don't have the CFM you need for 18 feet of ducting.

I have had good results with the Panasonic fan/heat/light units, and they are available as a special order from HD and other sources. They flow about 110 CFM, which is much better than the 50 CFM you get from a cheaper fan. If you install a combo unit that has both fan and heat, your wife will find it really convenient.

 

[Steve_P]

As said, to push air 18', you're going to need an industrial grade fan(s), which you most likely don't have. I have a couple of Panasonic fans, and they probably have only 6' of ducting to the roof vent and they're still only adequate.

 

[andyvh1959]

Pretty certain the fan is origianl to the house, built in 1973. So no specs to read on its capacity as it was way undersized to begin with back in 1973. Ducting is original to 1973, 18' of smooth rigid galvanized ducting to the eave. Ducting just, ends, inches from the eave, with no deflector box to direct the exhaust down through the soffit vent. So, IF any moist air gets that far it just blows against the backside of the cedar fascia, and I see no evidence of moisture there. So I expect the ducting is blocked which is why I have moisture issues on the btahroom ceiling now.

Yes, the old old bathroom fan is woefully inadequate, so I plan to replace it with a new fan and light unit. New ones have built in motion sensing night light and automatic start humidity sensor. The bathroom is 80 sq ft, which doesn't require a very large fan, but given it has to push the air 18' to the eave vent means I probably should upsize it capacity wise at least 1/2 as much, like sized for a 160 sq ft bathroom.

 

[ltusler]

I found the outlet flap at the fan housing stuck closed on mine once.

 

[PCustoms]

@andyvh1959 the fan is running, right?

 

[toolmiser]

I found the outlet flap at the fan housing stuck closed on mine once.

Same here

 

[The Cobbler]

I found the outlet flap at the fan housing stuck closed on mine once.

or lint sticking the damper closed on the unit itself

 

[16again]

Mine just blows about 2ft up into the attic. House was built in '58 and has a 36" gable vent on each side. I've been in this house 28 years and never had any issue.....no signs of wetness or mildew anywhere.

Same here. Mine's a little newer, built in 1970.

 

[Codyboy]

I found the outlet flap at the fan housing stuck closed on mine once.

I think mine sticks open sometimes.
I can turn off the fan and sometimes hear the clunk right away , sometimes it takes a minute, then , clunk.

I don't think 18ft of smooth pipe would be too much an issue.
OP never responded that I saw to my post about insulation and sealing around the box.
He only mentioned paint peeling and moisture around the fan. No different than a ceiling hvac register that has compromised insulation around it. It affects the sheet rock around it.
Is the rest of the ceiling dripping with moisture or just around the fan?

 

[rharman]

I had the opposite issue of the outlet flaps sticking. Mine were falling apart. Since the frame had been embedded in the stucco, replacing it would have been problematic.

I found this site and ordered replacement louvers. A great solution if any of you need it.

louverlovers.com

 

[etherhuffer]

Look up Fantech products. They really perform well, quiet. Our whole house has Fantech fans. Exterior 'puller' fans help move fan noise outside of house.

 

[fitter30]

Heres a bathroom cfm calculator. Most contractors put in a to small exhaust fan. 18' ft run 4" is a minimum size. Pick a fan that is for hi static.

Bathroom Fan CFM Calculator | Size Your Exhaust Fan

Free bathroom ventilation calculator. Size your exhaust fan correctly using CFM calculations based on room dimensions and ASHRAE standards. Prevent moisture issues.

westshorehome.com

 

[Tdbo]

I ran mine up to the ridge vent. Works well.
Also added a humidistat switch to the fan.
No more fogged mirrors, plus it clears excess humidity out when it is present, not just while showering.

 

[andyvh1959]

In my bathroom, yes the old fan is running, spins up just fine but if it puts out 50cfm in a bathroom needing at minimum 80cfm its no where near big enough. That and the fact the fan is at least 52 years old, I'm replacing it. Also since the new fan has an intergral anti-draft flap in the fan housing I will delete the flap in the discharge chute at the end of the 18' duct into the eave. And, since the dischargfe chute will direct the outflow down through the vented eave I don't want a flap there that could freeze shut in winter temps. I'll block off just the section of the eave between the rafters where the discharge chute will be so no outside strong wind blast cannot blow the bathroom exhaust air back into the attic.

As asked above: I don't think 18ft of smooth pipe would be too much an issue. I agree, but I may add a duct booster fan if needed later.
OP never responded that I saw to my post about insulation and sealing around the box. Pretty sure the original duct is blocked at the open end so the current fan is exhausting into whatever gap/leak is in the ducting which is just above the bathroom ceiling, hence the peeling paint, etc.
He only mentioned paint peeling and moisture around the fan. No different than a ceiling hvac register that has compromised insulation around it. It affects the sheet rock around it.
Is the rest of the ceiling dripping with moisture or just around the fan. Ceiling paint is bulged/peeling near the fan but not inline with the ducting. So I assume it is leaking at whatever gaps exist. I will replace that run of ducting with brand new one piece ductiing to reach across to an area in the attic where I can access the ducting which is currently buried in insulation. Any ducting joints will be sealed with good duct tape.

Once the fan and ducting is replaced I will repair the drywall as needed, which may mean I have to replace a section of drywall if the damage is more than just peeling paint (pretty likely it is more than just paint to repair).

 

[PoorUB]

As asked above: I don't think 18ft of smooth pipe would be too much an issue. I agree, but I may add a duct booster fan if needed later.

18 feet of what size duct? 3"? 4"? You will not get 50 CFM out of 18 feet of 4". If it is 3" you will never be happy with it. You might need to go to 5" duct.
Another issue, I don't know if anyone mentioned it, but moisture in the duct can be an issue. We often sealed up bathroom exhaust with a good caulk, and then insulated the duct. If you replace the duct, keep the seams up, caulk the joints and insulate it.

I put our bath fans on a timer. When we hop in for a shower we set the timer for an hour and that helps dry out the duct. It is probably not very energy conscious, but no moisture issues either.

 

[pbon]

I agree with the comments about the 18 foot run and a cheap low CFM fan. There are some good, quiet 100+ CFM fans that can do that run but they will cost more.

 

[jhelrey]

Are you leaving the fan on long enough? I have a 30 minute push button timer for mine and we try to keep the door for the bathroom cracked open if we have no guests.

 

[andyvh1959]

My wife runs the current fan the entire time she is in the shower and some time afterward.

The 18' long 4" duct currently in the ceiling and attic is straight, and all smooth ducting, no elbows, no rise. From what I've found (internet is always true right) 4" smooth ducting is good for up to 100 cfm. When I reinstall the ducting I will put it seam up, and caulk/tape all the seams. The entire run of ducting from the fan to the discharge hood will be insulated. The control unit for the fan features presets, and features a motion sensor/night lite and sensor to start the fan when a humidity preset is exceeded.

Looking at the fans sold at Menards; 60, 80, 100, 130 CFM fans all feature a 4" duct connection, regardless of four brand names. Once up to 150 cfm the duct connection upsizes to 6".